compositor-drm: remove dead assigment in drm_fb_create_dumb

ret is overwritten by drmModeAddFB2 call

(Found by clang source code analyzer)

Signed-off-by: Emre Ucan <eucan@de.adit-jv.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>

libweston/compositor-drm.c

@@ -891,8 +891,6 @@ drm_fb_create_dumb(struct drm_backend *b, int width, int height,
 	fb->height = height;
 	fb->fd = b->drm.fd;
 
-	ret = -1;
-
 	handles[0] = fb->handle;
 	pitches[0] = fb->stride;
 	offsets[0] = 0;