media: mtk-mdp: Check return value of of_clk_get

Check the return value of of_clk_get and print an error
message if not EPROBE_DEFER.

Signed-off-by: Matthias Brugger <mbrugger@suse.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>