stm32/flash: Remove FLASH_OPTR_DBANK condition in L4, H7 get_bank func.

This was added by mistake in 8f68e26f when
adding support for G4 MCUs, which does not using this get_bank() function.

FLASH_OPTR_DBANK is only defined on G4 and L4 MCUs, so on H7 this
FLASH_BANK_2 code was being wrongly excluded.
Signed-off-by: Damien George <damien@micropython.org>

ports/stm32/flash.c

@@ -140,20 +140,12 @@ static uint32_t get_bank(uint32_t addr) {
         if (addr < (FLASH_BASE + FLASH_BANK_SIZE)) {
             return FLASH_BANK_1;
         } else {
-            #if defined(FLASH_OPTR_DBANK)
             return FLASH_BANK_2;
-            #else
-            return 0;
-            #endif
         }
     } else {
         // bank swap
         if (addr < (FLASH_BASE + FLASH_BANK_SIZE)) {
-            #if defined(FLASH_OPTR_DBANK)
             return FLASH_BANK_2;
-            #else
-            return 0;
-            #endif
         } else {
             return FLASH_BANK_1;
         }