scsi: cxlflash: return -EFAULT if copy_from_user() fails

The copy_from/to_user() functions return the number of bytes remaining
to be copied but we had intended to return -EFAULT here.

Fixes: bc88ac47 ("scsi: cxlflash: Support AFU debug")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Matthew R. Ochs <mrochs@linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>