skd: Remove set-but-not-used local variables

skd: Remove set-but-not-used local variables

These variables have been detected by building with W=1. Declare
'acc' as __maybe_unused because most access_ok() implementations
ignore their first argument. This patch does not change any
functionality.

Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>