media: platform: Refactor mtk_jpeg_try_fmt_mplane()

The function of mtk_jpeg_adjust_fmt_mplane() equals
mtk_jpeg_g_fmt_vid_mplane(), so use mtk_jpeg_g_fmt_vid_mplane() to
replace it .
Delete the unused ctx parameter.
Using fourcc to distinguish between different formats is more generic,
because that jpeg enc will also use it.

Reviewed-by: Tomasz Figa <tfiga@chromium.org>
Signed-off-by: Xia Jiang <xia.jiang@mediatek.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>