[202205][Mellanox] Fix a typo in platform API

[stephenxs]

Why I did it

Fix a typo in chassis platform API which causes the following error

>>> import sonic_platform as P
>>> c = P.platform.Platform().get_chassis()
>>> sl = c.get_all_sfps()
>>> sl[0].get_lpmode()
Sep 28 07:48:33 INFO    LOG: Initializing SX log with STDOUT as output file.
False
>>> del c
Exception ignored in: <function Chassis.__del__ at 0x7f1d166ef8b0>
Traceback (most recent call last):
  File "/usr/local/lib/python3.9/dist-packages/sonic_platform/chassis.py", line 126, in __del__
    self.sfp_module.deinitialize_sdk_handle(sfp_module.SFP.shared_sdk_handle)
NameError: name 'sfp_module' is not defined

Signed-off-by: Stephen Sun stephens@nvidia.com

How I did it

Use self while using the SDK handle

How to verify it

Manual test

>>> import sonic_platform as P
>>> c = P.platform.Platform().get_chassis()
>>> sl = c.get_all_sfps()
>>> sl[0].get_lpmode()
Sep 28 07:45:41 INFO    LOG: Initializing SX log with STDOUT as output file.
False
>>> del c
>>>

Which release branch to backport (provide reason below if selected)

• 201811
• 201911
• 202006
• 202012
• 202106
• 202111
• 202205

Description for the changelog

Ensure to add label/tag for the feature raised.

Link to config_db schema for YANG module changes

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