kbuild: fix segmentation fault in modpost

If modpost was called manually with filenames without '/'
then modpost would segfault.
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

scripts/mod/modpost.c

@@ -1345,6 +1345,7 @@ static void add_depends(struct buffer *b, struct module *mod,
 	buf_printf(b, "__attribute__((section(\".modinfo\"))) =\n");
 	buf_printf(b, "\"depends=");
 	for (s = mod->unres; s; s = s->next) {
+		const char *p;
 		if (!s->module)
 			continue;
 
@@ -1352,8 +1353,11 @@ static void add_depends(struct buffer *b, struct module *mod,
 			continue;
 
 		s->module->seen = 1;
-		buf_printf(b, "%s%s", first ? "" : ",",
-			   strrchr(s->module->name, '/') + 1);
+		if ((p = strrchr(s->module->name, '/')) != NULL)
+			p++;
+		else
+			p = s->module->name;
+		buf_printf(b, "%s%s", first ? "" : ",", p);
 		first = 0;
 	}
 	buf_printf(b, "\";\n");