media: platform: Refactor mtk_jpeg_set_default_params()

Call mtk_jpeg_try_fmt_mplane() to replace the original computation of
sizeimage and bytesperline, because that mtk_jpeg_try_fmt_mplane()
already did 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>