log: Fix reporting OOM error incorrectly when defining a logging filter

When a new filter is being defined, the return code is not handled properly,
thus triggering OOM error reporting routine (bug introduced by 51b2606f).
Signed-off-by: NErik Skultety <eskultet@redhat.com>

src/util/virlog.c

@@ -335,11 +335,12 @@ virLogDefineFilter(const char *match,
         goto cleanup;
 
     virLogFiltersSerial++;
+    ret = virLogNbFilters - 1;
  cleanup:
     virLogUnlock();
     if (ret < 0)
         virReportOOMError();
-    return virLogNbFilters;
+    return ret;
 }
 
 /**