drm backend: overflow fixes

These operations are done in 32-bit arithmetics before being casted to 64-bit,
thus can overflow before the cast.
Casting early fixes the issue.

Found through static analysis

backend/drm/atomic.c

@@ -83,8 +83,8 @@ static void set_plane_props(struct atomic *atom, struct wlr_drm_plane *plane,
 	// The src_* properties are in 16.16 fixed point
 	atomic_add(atom, id, props->src_x, 0);
 	atomic_add(atom, id, props->src_y, 0);
-	atomic_add(atom, id, props->src_w, plane->surf.width << 16);
+	atomic_add(atom, id, props->src_w, (uint64_t)plane->surf.width << 16);
-	atomic_add(atom, id, props->src_h, plane->surf.height << 16);
+	atomic_add(atom, id, props->src_h, (uint64_t)plane->surf.height << 16);
 	atomic_add(atom, id, props->crtc_w, plane->surf.width);
 	atomic_add(atom, id, props->crtc_h, plane->surf.height);
 	atomic_add(atom, id, props->fb_id, fb_id);

backend/drm/drm.c

@@ -973,7 +973,7 @@ int handle_drm_event(int fd, uint32_t mask, void *data) {
 }
 
 void restore_drm_outputs(struct wlr_drm_backend *drm) {
-	uint64_t to_close = (1 << wl_list_length(&drm->outputs)) - 1;
+	uint64_t to_close = (1L << wl_list_length(&drm->outputs)) - 1;
 
 	struct wlr_drm_connector *conn;
 	wl_list_for_each(conn, &drm->outputs, link) {