fbdev: fsl-diu-fb: add missing device_remove_file()

[ Upstream commit 86d16cd1 ]

Call device_remove_file() when driver remove.

Signed-off-by: Shixiong Ou <oushixiong@kylinos.cn>
Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>