Fix apparent STM32G0 flashing issue. (#797)

* Add simple read/write support for STM32WB55 chips.

* Clean up and unify G0/WB erase/program operations.

* Fix apparent issue with STM32G0 flashing.

src/common.c

@@ -1766,7 +1766,7 @@ int stlink_erase_flash_page(stlink_t *sl, stm32_addr_t flashaddr)
             uint32_t flash_page = ((flashaddr - STM32_FLASH_BASE) / sl->flash_pgsz);
             stlink_read_debug32(sl, STM32G0_FLASH_CR, &val);
             // sec 3.7.5 - PNB[5:0] is offset by 3. PER is 0x2.
-            val |= ((flash_page & 0x3F) << 3);
+            val = ((flash_page & 0x3F) << 3) | ( 1 << FLASH_CR_PER );
             stlink_write_debug32(sl, STM32G0_FLASH_CR, val);
         }