stm32: stm32_flash: add memory barrier during flash write

After writing data to flash space, next instruction is checking if flash
controller is busy writing to the flash memory. Memory barrier is required here
to avoid transaction re-ordering for data write and busy status check.

Signed-off-by: Vikas Manocha <vikas.manocha@st.com>

drivers/mtd/stm32_flash.c

@@ -137,6 +137,10 @@ int write_buff(flash_info_t *info, uchar *src, ulong addr, ulong cnt)
 	/* To make things simple use byte writes only */
 	for (i = 0; i < cnt; i++) {
 		*(uchar *)(addr + i) = src[i];
+		/*  avoid re-ordering flash data write and busy status
+		 *  check as flash memory space attributes are generally Normal
+		 */
+		mb();
 		while (readl(&STM32_FLASH->sr) & STM32_FLASH_SR_BSY)
 			;
 	}