Fix some build errors

backend/backend.c

@@ -6,7 +6,7 @@
 #include <wlr/session.h>
 #include <wlr/backend/interface.h>
 #include "common/log.h"
-#include "backend/drm/backend.h"
+#include "backend/drm.h"
 
 struct wlr_backend *wlr_backend_create(const struct wlr_backend_impl *impl,
 		struct wlr_backend_state *state) {

include/backend/drm.h

@@ -17,7 +17,6 @@
 #include "backend/egl.h"
 #include "backend/udev.h"
 #include "event.h"
-#include "drm.h"
 
 struct wlr_drm_renderer {
 	int fd;