Initialize get_resolvconf_addr variable rv to NULL

Getting warning compiling for Android:

./util.c:35:6: warning: variable 'rv' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
        if (sscanf(buf, "%15s", addr) == 1)
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./util.c:79:9: note: uninitialized use occurs here
        return rv;
               ^~

src/util.c

@@ -22,7 +22,7 @@
 char *get_resolvconf_addr(void)
 {
 	static char addr[16];
-	char *rv;
+	char *rv = NULL;
 #ifndef WINDOWS32
 	char buf[80];
 	FILE *fp;