scsi/ufs: Rename a 'dir' argument into 'op'

Improve consistency of the kernel code by renaming a request operation
argument from 'dir' into 'op'.

Reviewed-by: Avri Altman <avri.altman@wdc.com>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20220714180729.1065367-44-bvanassche@acm.org


Signed-off-by: Jens Axboe <axboe@kernel.dk>