Audio route: log fopen xml_patch failure errno

Vts fail a log because of this open. It is likely a result of previous
leaks (EMFILE) but in order to be sure, log fopen errno value in case of
failure.

Test: play music
Bug: 36311550

Change-Id: I834b346d5387b142d7bd0bd9c1c6d9b9e2a85339
Signed-off-by: Kevin Rocard <krocard@google.com>
diff --git a/audio_route/audio_route.c b/audio_route/audio_route.c
index c13b278..89b076b 100644
--- a/audio_route/audio_route.c
+++ b/audio_route/audio_route.c
@@ -881,7 +881,7 @@
     file = fopen(xml_path, "r");
 
     if (!file) {
-        ALOGE("Failed to open %s", xml_path);
+        ALOGE("Failed to open %s: %s", xml_path, strerror(errno));
         goto err_fopen;
     }