dfu: Fix handling of UBI partitions in MTD backend

For UBI partitions ("partubi" in dfu_alt_info), dfu_fill_entity_mtd sets
the mtd.ubi flag; however other functions incorrectly check for nand.ubi
instead. Fix this by checking for the correct flag.

Signed-off-by: Guillermo Rodriguez <guille.rodriguez@gmail.com>
Cc: Lukasz Majewski <lukma@denx.de>
Reviewed-by: Patrick Delaunay <patrick.delaunay@st.com>
diff --git a/drivers/dfu/dfu_mtd.c b/drivers/dfu/dfu_mtd.c
index b34975d..ca67585 100644
--- a/drivers/dfu/dfu_mtd.c
+++ b/drivers/dfu/dfu_mtd.c
@@ -204,7 +204,7 @@
 	int ret;
 
 	/* in case of ubi partition, erase rest of the partition */
-	if (dfu->data.nand.ubi) {
+	if (dfu->data.mtd.ubi) {
 		struct erase_info erase_op = {};
 
 		erase_op.mtd = dfu->data.mtd.info;
@@ -242,7 +242,7 @@
 	 * ubi partition, as sectors which are not used need
 	 * to be erased
 	 */
-	if (dfu->data.nand.ubi)
+	if (dfu->data.mtd.ubi)
 		return DFU_MANIFEST_POLL_TIMEOUT;
 
 	return DFU_DEFAULT_POLL_TIMEOUT;