hwc: Use proper typecasts

- Remove compiler warnings
- Use proper typecasts

Change-Id: I7391f32ae31283239f5cebb93b02f3ce3a5c99f3
diff --git a/libhwcomposer/hwc_uevents.cpp b/libhwcomposer/hwc_uevents.cpp
index 7bc29bc..e1f7827 100644
--- a/libhwcomposer/hwc_uevents.cpp
+++ b/libhwcomposer/hwc_uevents.cpp
@@ -323,7 +323,7 @@
     }
 
     while(1) {
-        len = uevent_next_event(udata, sizeof(udata) - 2);
+        len = uevent_next_event(udata, (int)sizeof(udata) - 2);
         handle_uevent(ctx, udata, len);
     }