scsi: cxlflash: Remove an unnecessary NULL check

The "cmd" pointer was already dereferenced a couple lines earlier so this
NULL check is too late.  Fortunately, the pointer can never be NULL and the
check can be removed.

Link: https://lore.kernel.org/r/20200605110258.GD978434@mwanda


Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>