scsi: megaraid_sas: Use struct_size() in code related to struct MR_PD_CFG_SEQ_NUM_SYNC

Prefer struct_size() over open-coded versions of idiom:

        sizeof(struct-with-flex-array) + sizeof(type-of-flex-array) * count

where count is the max number of items the flexible array is supposed to
have.

Link: https://github.com/KSPP/linux/issues/160
Link: https://lore.kernel.org/r/b215f4760f0e8fbe5fc35be20f2487e89924424d.1660592640.git.gustavoars@kernel.orgReviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/megaraid/megaraid_sas_base.c

@@ -5790,10 +5790,10 @@ megasas_setup_jbod_map(struct megasas_instance *instance)
 {
 	int i;
 	struct fusion_context *fusion = instance->ctrl_context;
-	u32 pd_seq_map_sz;
+	size_t pd_seq_map_sz;
 
-	pd_seq_map_sz = sizeof(struct MR_PD_CFG_SEQ_NUM_SYNC) +
-		(sizeof(struct MR_PD_CFG_SEQ) * MAX_PHYSICAL_DEVICES);
+	pd_seq_map_sz = struct_size((struct MR_PD_CFG_SEQ_NUM_SYNC *)0, seq,
+				    MAX_PHYSICAL_DEVICES);
 
 	instance->use_seqnum_jbod_fp =
 		instance->support_seqnum_jbod_fp;
@@ -7972,7 +7972,7 @@ static void megasas_detach_one(struct pci_dev *pdev)
 	struct Scsi_Host *host;
 	struct megasas_instance *instance;
 	struct fusion_context *fusion;
-	u32 pd_seq_map_sz;
+	size_t pd_seq_map_sz;
 
 	instance = pci_get_drvdata(pdev);
 
@@ -8044,9 +8044,9 @@ static void megasas_detach_one(struct pci_dev *pdev)
 
 	if (instance->adapter_type != MFI_SERIES) {
 		megasas_release_fusion(instance);
-		pd_seq_map_sz = sizeof(struct MR_PD_CFG_SEQ_NUM_SYNC) +
-				(sizeof(struct MR_PD_CFG_SEQ) *
-					MAX_PHYSICAL_DEVICES);
+		pd_seq_map_sz =
+			struct_size((struct MR_PD_CFG_SEQ_NUM_SYNC *)0,
+				    seq, MAX_PHYSICAL_DEVICES);
 		for (i = 0; i < 2 ; i++) {
 			if (fusion->ld_map[i])
 				dma_free_coherent(&instance->pdev->dev,