do_mounts: allow UBI root device name

Similarly to MTD devices, allow UBI devices.

Signed-off-by: Adrian Hunter <ext-adrian.hunter@nokia.com>
diff --git a/init/do_mounts.c b/init/do_mounts.c
index 660c1e5..a1de1bf 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -372,7 +372,8 @@
 
 	if (saved_root_name[0]) {
 		root_device_name = saved_root_name;
-		if (!strncmp(root_device_name, "mtd", 3)) {
+		if (!strncmp(root_device_name, "mtd", 3) ||
+		    !strncmp(root_device_name, "ubi", 3)) {
 			mount_block_root(root_device_name, root_mountflags);
 			goto out;
 		}