scsi: sd: Fix kdoc comment format

Fix the kdoc comment of the function sd_ioctl_common() to avoid a compiler
warning when compiling with W=1.

No functional changes.

Link: https://lore.kernel.org/r/20200706123354.452047-1-damien.lemoal@wdc.comSigned-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/sd.c

@@ -1479,7 +1479,7 @@ static int sd_getgeo(struct block_device *bdev, struct hd_geometry *geo)
  *	@bdev: target block device
  *	@mode: FMODE_* mask
  *	@cmd: ioctl command number
- *	@arg: this is third argument given to ioctl(2) system call.
+ *	@p: this is third argument given to ioctl(2) system call.
  *	Often contains a pointer.
  *
  *	Returns 0 if successful (some ioctls return positive numbers on