Avoid assertion in check_interrupts_property()

If running on a tree with an 'interrupt-parent' property which contains
an invalid phandle (0 or -1, not merely for a node which doesn't exist),
then check_interrupts_property() will trip the assertion in
get_node_by_phandle().

There's logic that almost detects this, but it only handles the overlay
case, where we can't fully check because the links will be fixed up later.

For the non-overlay case, this is definitely a bad property, but we
shouldn't crash.  Fix it by failing the check early.

Fixes: c1e55a5513 ("checks: fix handling of unresolved phandles for dts plugins")
Fixes: ee3d26f696 ("checks: add interrupts property check")
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

checks.c

@@ -1580,10 +1580,14 @@ static void check_interrupts_property(struct check *c,
 		prop = get_property(parent, "interrupt-parent");
 		if (prop) {
 			phandle = propval_cell(prop);
-			/* Give up if this is an overlay with external references */
-			if ((phandle == 0 || phandle == -1) &&
-			    (dti->dtsflags & DTSF_PLUGIN))
+			if ((phandle == 0) || (phandle == -1)) {
+				/* Give up if this is an overlay with
+				 * external references */
+				if (dti->dtsflags & DTSF_PLUGIN)
 					return;
+				FAIL_PROP(c, dti, parent, prop, "Invalid phandle");
+				continue;
+			}
 
 			irq_node = get_node_by_phandle(root, phandle);
 			if (!irq_node) {