RAS: ras_common: Add null pointer check for error record probe function

Add a null pointer check for the error record probe
function -- avoids a panic in case a platform has not defined it.

Change-Id: I1139fa0df33297a12ec16615cacd07540925f991
Signed-off-by: Sughosh Ganu <sughosh.ganu@arm.com>
diff --git a/lib/extensions/ras/ras_common.c b/lib/extensions/ras/ras_common.c
index 0335a7b..5a2b43c 100644
--- a/lib/extensions/ras/ras_common.c
+++ b/lib/extensions/ras/ras_common.c
@@ -114,9 +114,10 @@
 		panic();
 	}
 
-
-	ret = selected->err_record->probe(selected->err_record, &probe_data);
-	assert(ret != 0);
+	if (selected->err_record->probe) {
+		ret = selected->err_record->probe(selected->err_record, &probe_data);
+		assert(ret != 0);
+	}
 
 	/* Call error handler for the record group */
 	assert(selected->err_record->handler != NULL);