dfu:usb:fix: Read the "filesize" environment variable only when file read

The "filesize" environment variable shall be read only when relevant
file is read.

Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Reviewed-by: Marek Vasut <marex@denx.de>

drivers/dfu/dfu_mmc.c

@@ -89,7 +89,7 @@ static int mmc_file_op(enum dfu_mmc_op op, struct dfu_entity *dfu,
 		return ret;
 	}
 
-	if (dfu->layout != DFU_RAW_ADDR) {
+	if (dfu->layout != DFU_RAW_ADDR && op == DFU_OP_READ) {
 		str_env = getenv("filesize");
 		if (str_env == NULL) {
 			puts("dfu: Wrong file size!\n");