scsi: megaraid_sas: Add flexible array member for SGLs

struct MPI2_RAID_SCSI_IO_REQUEST ends with a single SGL, but expects to
copy multiple. Add a flexible array member so the compiler can reason about
the size of the memcpy(). This will avoid the run-time false positive
warning:

  memcpy: detected field-spanning write (size 128) of single field "&r1_cmd->io_request->SGL" at drivers/scsi/megaraid/megaraid_sas_fusion.c:3326 (size 16)

This change results in no binary output differences.
Reported-by: Holger Kiehl <Holger.Kiehl@dwd.de>
Link: https://lore.kernel.org/all/88de8faa-56c4-693d-2d3-67152ee72057@diagnostix.dwd.de/
Cc: Kashyap Desai <kashyap.desai@broadcom.com>
Cc: Sumit Saxena <sumit.saxena@broadcom.com>
Cc: Shivasharan S <shivasharan.srikanteshwara@broadcom.com>
Cc: "James E.J. Bottomley" <jejb@linux.ibm.com>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>
Cc: megaraidlinux.pdl@broadcom.com
Cc: linux-scsi@vger.kernel.org
Link: https://lore.kernel.org/r/20230106053153.never.999-kees@kernel.orgSigned-off-by: Kees Cook <keescook@chromium.org>
Tested-by: Holger Kiehl <Holger.Kiehl@dwd.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/megaraid/megaraid_sas_fusion.c

@@ -3323,7 +3323,7 @@ static void megasas_prepare_secondRaid1_IO(struct megasas_instance *instance,
 	/* copy the io request frame as well as 8 SGEs data for r1 command*/
 	memcpy(r1_cmd->io_request, cmd->io_request,
 	       (sizeof(struct MPI2_RAID_SCSI_IO_REQUEST)));
-	memcpy(&r1_cmd->io_request->SGL, &cmd->io_request->SGL,
+	memcpy(r1_cmd->io_request->SGLs, cmd->io_request->SGLs,
 	       (fusion->max_sge_in_main_msg * sizeof(union MPI2_SGE_IO_UNION)));
 	/*sense buffer is different for r1 command*/
 	r1_cmd->io_request->SenseBufferLowAddress =

drivers/scsi/megaraid/megaraid_sas_fusion.h

@@ -526,7 +526,10 @@ struct MPI2_RAID_SCSI_IO_REQUEST {
 	__le32			Control;                        /* 0x3C */
 	union MPI2_SCSI_IO_CDB_UNION  CDB;			/* 0x40 */
 	union RAID_CONTEXT_UNION RaidContext;  /* 0x60 */
-	union MPI2_SGE_IO_UNION       SGL;			/* 0x80 */
+	union {
+		union MPI2_SGE_IO_UNION       SGL;		/* 0x80 */
+		DECLARE_FLEX_ARRAY(union MPI2_SGE_IO_UNION, SGLs);
+	};
 };
 
 /*