libusbhost: Fix issue of multiple inotify event at same time.

libusbhost can handle multiple inotify events at same time on Kit kat.
In original implementation, the function-level ret is assigned with
length of read and used for while loop.
if want to add a new watch for subdirectory,inotify_add_watch will
update the function-level ret with watch descriptor.
It impact on while loop to do exit.

Add local result to avoid it.

Change-Id: I101041ccfd54eaac14969a45e90ab2e49bdff578
Signed-off-by: Bo Huang <bo.b.huang@intel.com>
diff --git a/libusbhost/usbhost.c b/libusbhost/usbhost.c
index 8be393e..cd8000a 100644
--- a/libusbhost/usbhost.c
+++ b/libusbhost/usbhost.c
@@ -263,11 +263,12 @@
                 D("%s subdirectory %s: index: %d\n", (event->mask & IN_CREATE) ?
                         "new" : "gone", path, i);
                 if (i > 0 && i < MAX_USBFS_WD_COUNT) {
+                    int local_ret = 0;
                     if (event->mask & IN_CREATE) {
-                        ret = inotify_add_watch(context->fd, path,
+                        local_ret = inotify_add_watch(context->fd, path,
                                 IN_CREATE | IN_DELETE);
-                        if (ret >= 0)
-                            context->wds[i] = ret;
+                        if (local_ret >= 0)
+                            context->wds[i] = local_ret;
                         done = find_existing_devices_bus(path, context->cb_added,
                                 context->data);
                     } else if (event->mask & IN_DELETE) {