io_uring: fix typo in io_uring.h comment

Just a basic s/thig/this swap, fixing up a typo introduced by a commit
added in the 6.1 release.

Fixes: 9cda70f6 ("io_uring: introduce fixed buffer support for io_uring_cmd")
Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/uapi/linux/io_uring.h

@@ -222,7 +222,7 @@ enum io_uring_op {
 
 /*
  * sqe->uring_cmd_flags
- * IORING_URING_CMD_FIXED	use registered buffer; pass thig flag
+ * IORING_URING_CMD_FIXED	use registered buffer; pass this flag
  *				along with setting sqe->buf_index.
  */
 #define IORING_URING_CMD_FIXED	(1U << 0)