scsi: vmw_pscsi: Fix use-after-free in pvscsi_queue_lck()

Once we unlock adapter->hw_lock in pvscsi_queue_lck() nothing prevents just
queued scsi_cmnd from completing and freeing the request. Thus cmd->cmnd[0]
dereference can dereference already freed request leading to kernel crashes
or other issues (which one of our customers observed). Store cmd->cmnd[0]
in a local variable before unlocking adapter->hw_lock to fix the issue.

CC: <stable@vger.kernel.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Ewan D. Milne <emilne@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>