dm: cleanup double word in comment

Remove the second 'a'.

Signed-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

Author: Tom Rix

include/linux/device-mapper.h

@@ -358,7 +358,7 @@ struct dm_target {
 	bool limit_swap_bios:1;
 
 	/*
-	 * Set if this target implements a a zoned device and needs emulation of
+	 * Set if this target implements a zoned device and needs emulation of
 	 * zone append operations using regular writes.
 	 */
 	bool emulate_zone_append:1;