libyang MAINTENANCE fox uninitialized vars warnings

Even though they all are false-positives.
diff --git a/src/xml.c b/src/xml.c
index 22afda5..02f7f4b 100644
--- a/src/xml.c
+++ b/src/xml.c
@@ -1213,6 +1213,7 @@
         if (ptr1[0] != ptr2[0]) {
             /* it can be a start of prefix that maps to the same module */
             ns1 = ns2 = NULL;
+            u1 = u2 = 0;
             if (prefs1) {
                 /* find module of the first prefix, if any */
                 LY_ARRAY_FOR(prefs1, u1) {