mpi3mr: Build with gcc12 by being more explicit about conditions

Help the flow analysis in gcc12 by initializing scsi_reply to NULL and
testing it along with sense_buf. Sense buf should be non-null only in
this code path, but might also be non-null if the PA for is somehow set
to zero. I debated adding an assert for the latter, but opted to instead
preserve existing behavior.

Also set host_diagnostic to 0. gcc12 can't quite realize that we only
test it after we've been through this loop at least once to report an
error condition. Initialize to 0 to avoid a diagnostic.

Sponsored by:		Netflix

sys/dev/mpi3mr/mpi3mr.c

@@ -4487,7 +4487,7 @@ static void mpi3mr_process_admin_reply_desc(struct mpi3mr_softc *sc,
 	Mpi3SuccessReplyDescriptor_t *success_desc;
 	Mpi3DefaultReply_t *def_reply = NULL;
 	struct mpi3mr_drvr_cmd *cmdptr = NULL;
-	Mpi3SCSIIOReply_t *scsi_reply;
+	Mpi3SCSIIOReply_t *scsi_reply = NULL;
 	U8 *sense_buf = NULL;
 
 	*reply_dma = 0;
@@ -4590,7 +4590,7 @@ static void mpi3mr_process_admin_reply_desc(struct mpi3mr_softc *sc,
 		}
 	}
 out:
-	if (sense_buf != NULL)
+	if (scsi_reply != NULL && sense_buf != NULL)
 		mpi3mr_repost_sense_buf(sc,
 		    scsi_reply->SenseDataBufferAddress);
 	return;
@@ -6162,7 +6162,7 @@ static int mpi3mr_issue_reset(struct mpi3mr_softc *sc, U16 reset_type,
 {
 	int retval = -1;
 	U8 unlock_retry_count = 0;
-	U32 host_diagnostic, ioc_status, ioc_config, scratch_pad0;
+	U32 host_diagnostic = 0, ioc_status, ioc_config, scratch_pad0;
 	U32 timeout = MPI3MR_RESET_ACK_TIMEOUT * 10;
 
 	if ((reset_type != MPI3_SYSIF_HOST_DIAG_RESET_ACTION_SOFT_RESET) &&