media: s5p-mfc: Fix display delay control creation

v4l2_ctrl_new_std() fails if the caller provides no 'step' parameter for
integer control, so define it to fix following error:

s5p_mfc_dec_ctrls_setup:1166: Adding control (1) failed

Fixes: c3042bff ("media: s5p-mfc: Use display delay and display enable std controls")
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>