parser: add TYPE_STRING marker to path references

Path references are also a string, so add TYPE_STRING marker in addition
to REF_PATH.

Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

dtc-parser.y

@@ -287,6 +287,7 @@ propdata:
 		}
 	| propdataprefix DT_REF
 		{
+			$1 = data_add_marker($1, TYPE_STRING, $2);
 			$$ = data_add_marker($1, REF_PATH, $2);
 		}
 	| propdataprefix DT_INCBIN '(' DT_STRING ',' integer_prim ',' integer_prim ')'