stmhal: Process storage idle tick handler in different slot to DMA.

stmhal/storage.h

@@ -27,7 +27,7 @@
 #define FLASH_BLOCK_SIZE (512)
 
 #define STORAGE_SYSTICK_MASK    (0x1ff) // 512ms
-#define STORAGE_IDLE_TICK(tick) (((tick) & STORAGE_SYSTICK_MASK) == 0)
+#define STORAGE_IDLE_TICK(tick) (((tick) & STORAGE_SYSTICK_MASK) == 2)
 
 void storage_init(void);
 uint32_t storage_get_block_size(void);