scsi: cxlflash: fix assignment of the backend operations

scsi: cxlflash: fix assignment of the backend operations

commit cd43c221bb5e ("scsi: cxlflash: Isolate external module
dependencies") introduced the use of ifdefs to avoid compilation errors
when one of the possible backend driver, CXL or OCXL, is not compiled.

Unfortunately, the wrong defines are used and the backend ops are never
assigned, leading to a kernel crash in any case when the cxlflash module is
loaded.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Acked-by: Matthew R. Ochs <mrochs@linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>