scsi: cxlflash: Adapter context init can return error

Adapter context creation can return either NULL or an error pointer.
Updating the check condition to reflect this.

Signed-off-by: Uma Krishnan <ukrishn@linux.vnet.ibm.com>
Acked-by: Matthew R. Ochs <mrochs@linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>