hwc: Fix unchecked return value

Check the return value of uevent_init function
and return on error.

Change-Id: I9dfca0ed84cbe5f1abf5716c5deed7808aa046ea
diff --git a/libhwcomposer/hwc_uevents.cpp b/libhwcomposer/hwc_uevents.cpp
index 8c3d00d..88df542 100644
--- a/libhwcomposer/hwc_uevents.cpp
+++ b/libhwcomposer/hwc_uevents.cpp
@@ -309,7 +309,10 @@
     char thread_name[64] = HWC_UEVENT_THREAD_NAME;
     prctl(PR_SET_NAME, (unsigned long) &thread_name, 0, 0, 0);
     setpriority(PRIO_PROCESS, 0, HAL_PRIORITY_URGENT_DISPLAY);
-    uevent_init();
+    if(!uevent_init()) {
+        ALOGE("%s: failed to init uevent ",__FUNCTION__);
+        return NULL;
+    }
 
     while(1) {
         len = uevent_next_event(udata, sizeof(udata) - 2);