libata: fix a typo in comment

poitner -> pointer.
Signed-off-by: Chengguang Xu <cgxu519@gmx.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/ata/libata-scsi.c

@@ -2990,7 +2990,7 @@ static unsigned int atapi_xlat(struct ata_queued_cmd *qc)
 	 * This inconsistency confuses several controllers which
 	 * perform PIO using DMA such as Intel AHCIs and sil3124/32.
 	 * These controllers use actual number of transferred bytes to
-	 * update DMA poitner and transfer of 4n+2 bytes make those
+	 * update DMA pointer and transfer of 4n+2 bytes make those
 	 * controller push DMA pointer by 4n+4 bytes because SATA data
 	 * FISes are aligned to 4 bytes.  This causes data corruption
 	 * and buffer overrun.