scsi: megaraid_sas: Avoid a couple -Wflex-array-member-not-at-end warnings

scsi: megaraid_sas: Avoid a couple -Wflex-array-member-not-at-end warnings

-Wflex-array-member-not-at-end was introduced in GCC-14, and we are
getting ready to enable it, globally.

Use the new TRAILING_OVERLAP() helper to fix the following warnings:

drivers/scsi/megaraid/megaraid_sas_fusion.h:1153:31: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/scsi/megaraid/megaraid_sas_fusion.h:1198:32: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

This helper creates a union between a flexible-array member (FAM) and a
set of MEMBERS that would otherwise follow it --in this case 'struct
MR_LD_SPAN_MAP ldSpanMap[MAX_LOGICAL_DRIVES_DYN]' and 'struct
MR_LD_SPAN_MAP ldSpanMap[MAX_LOGICAL_DRIVES]' in the corresponding
structures.

This overlays the trailing members onto the FAM (struct MR_LD_SPAN_MAP
ldSpanMap[];) while keeping the FAM and the start of MEMBERS aligned.

The static_assert() ensures this alignment remains, and it's
intentionally placed inmediately after the corresponding structures --no
blank line in between.

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://patch.msgid.link/aM1E7Xa8qYdZ598N@kspp
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>