STM32 QSPI: Use defines for setting address size

[LMESTM]

Description (required)

A small clean-up Pull Request, to align with rest of the code following recent changes in QSPI.

Summary of change (What the change is for and why)

The change follows recent updates and can be considered a cosmetic change but should be future proof for any new STM32 devices with QSPI.

Documentation (Details of any document updates required)

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Pull request type (required)

[x] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

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Test results (required)

Tested fine on DISCO_L475VG_IOT01A

+-----------------------------+---------------------+---------------------+--------+--------------------+-------------+
| target                      | platform_name       | test suite          | result | elapsed_time (sec) | copy_method |
+-----------------------------+---------------------+---------------------+--------+--------------------+-------------+
| DISCO_L475VG_IOT01A-GCC_ARM | DISCO_L475VG_IOT01A | tests-mbed_hal-qspi | OK     | 37.78              | default     |
+-----------------------------+---------------------+---------------------+--------+--------------------+-------------+

+-----------------------------+---------------------+---------------------------------------------------------+--------+--------------------+-------------+
| target                      | platform_name       | test suite                                              | result | elapsed_time (sec) | copy_method |
+-----------------------------+---------------------+---------------------------------------------------------+--------+--------------------+-------------+
| DISCO_L475VG_IOT01A-GCC_ARM | DISCO_L475VG_IOT01A | features-storage-tests-blockdevice-general_block_device | OK     | 38.42              | default     |
+-----------------------------+---------------------+---------------------------------------------------------+--------+--------------------+-------------+

[] No Tests required for this change (E.g docs only update)
[] Covered by existing mbed-os tests (Greentea or Unittest)
[] Tests / results supplied as part of this PR

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Reviewers (optional)

@jeromecoutant

[jeromecoutant]

ST CI OK also with DISCO_F769NI and DISCO_F746NG (other embedded QSPI memories)

[0xc0170]

CI started

[mbed-ci]

Test run: SUCCESS

Summary: 11 of 11 test jobs passed
Build number : 1
Build artifacts