mtd: ubi: drop unexpected word 'a' in comments

there is an unexpected word 'a' in the comments that need to be dropped

file - drivers/mtd/ubi/vmt.c
line - 626,779

* Returns zero if volume is all right and a a negative error code if not.

changed to:

* Returns zero if volume is all right and a negative error code if not.
Signed-off-by: Jiang Jian <jiangjian@cdjrlc.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

drivers/mtd/ubi/vmt.c

@@ -623,7 +623,7 @@ void ubi_free_volume(struct ubi_device *ubi, struct ubi_volume *vol)
  * @ubi: UBI device description object
  * @vol_id: volume ID
  *
- * Returns zero if volume is all right and a a negative error code if not.
+ * Returns zero if volume is all right and a negative error code if not.
  */
 static int self_check_volume(struct ubi_device *ubi, int vol_id)
 {
@@ -776,7 +776,7 @@ static int self_check_volume(struct ubi_device *ubi, int vol_id)
  * self_check_volumes - check information about all volumes.
  * @ubi: UBI device description object
  *
- * Returns zero if volumes are all right and a a negative error code if not.
+ * Returns zero if volumes are all right and a negative error code if not.
  */
 static int self_check_volumes(struct ubi_device *ubi)
 {