media: platform: s5p-mfc: Fix adding a standard frame skip mode control

Add proper control type to the recently introduced
V4L2_CID_MPEG_VIDEO_FRAME_SKIP_MODE control. This will forward it to
v4l2_ctrl_new_std_menu() not v4l2_ctrl_new_std(), what causes the
failure. This fixes the following warning during driver initialization:

s5p_mfc_enc_ctrls_setup:2671: Adding control (18) failed
s5p_mfc_open:811: Failed to setup mfc controls

Fixes: ef56b3ee ("media: s5p-mfc: Use standard frame skip mode control")
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>