stm32/mboot: Always check the magic number to enter filesystem loading.

Even if MBOOT_FSLOAD is disabled, mboot should still check for 0x70ad0080
so it can immediately return to the application if this feature is not
enabled.  Otherwise mboot will get stuck in DFU mode.

Signed-off-by: Damien George <damien@micropython.org>

ports/stm32/mboot/main.c

@@ -1539,8 +1539,8 @@ enter_bootloader:
     mboot_pack_init();
     #endif
 
-    #if MBOOT_FSLOAD
     if ((initial_r0 & 0xffffff80) == 0x70ad0080) {
+        #if MBOOT_FSLOAD
         // Application passed through elements, validate then process them
         const uint8_t *elem_end = elem_search(ELEM_DATA_START, ELEM_TYPE_END);
         if (elem_end != NULL && elem_end[-1] == 0) {
@@ -1553,11 +1553,11 @@ enter_bootloader:
                 *status_ptr = ret;
             }
         }
+        #endif
         // Always reset because the application is expecting to resume
         led_state_all(0);
         leave_bootloader();
     }
-    #endif
 
     dfu_init();