cxl/cper: Fix non-ACPI-APEI-GHES build

cxl/cper: Fix non-ACPI-APEI-GHES build

If ACPI_APEI_GHES is not configured the [un]register work functions are
not properly declared.

0day notices that the cxl_cper_register_work() declaration in the
CONFIG_ACPI_APEI_GHES=n is broken, fix it to be typical nop stub.

Reported-by: kernel test robot <lkp@intel.com>
Closes: http://lore.kernel.org/r/202405012230.6kXItWen-lkp@intel.com
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Link: https://lore.kernel.org/r/20240501-cper-fix-0day-v1-1-c0b0056eafbc@intel.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>