drm/udl: Clean up Makefile

Clean up Makefile before listing new object files. No functional
changes.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240510154841.11370-4-tzimmermann@suse.de

drivers/gpu/drm/udl/Makefile

 # SPDX-License-Identifier: GPL-2.0-only
-udl-y := udl_drv.o udl_modeset.o udl_main.o udl_transfer.o
+
+udl-y := \
+	udl_drv.o \
+	udl_main.o \
+	udl_modeset.o \
+	udl_transfer.o
 
 obj-$(CONFIG_DRM_UDL) := udl.o