compositor-drm: Stop sending uninit data to the kernel

Valgrind noticed that we send uninit data to drmModeAddFB2.  While
the kernel should never read this (because of the plane format),
it's probably still nicer to zero the data before we send it.

Signed-off-by: Derek Foreman <derekf@osg.samsung.com>
Reviewed-by: Yong Bakos <ybakos@humanoriented.com>

libweston/compositor-drm.c

@@ -394,7 +394,7 @@ drm_fb_get_from_bo(struct gbm_bo *bo,
 {
 	struct drm_fb *fb = gbm_bo_get_user_data(bo);
 	uint32_t width, height;
-	uint32_t handles[4], pitches[4], offsets[4];
+	uint32_t handles[4] = { 0 }, pitches[4] = { 0 }, offsets[4] = { 0 };
 	int ret;
 
 	if (fb)