media: uapi: HEVC: Change pic_order_cnt definition in v4l2_hevc_dpb_entry

The HEVC specification describes the following:
"PicOrderCntVal is derived as follows:
PicOrderCntVal = PicOrderCntMsb + slice_pic_order_cnt_lsb
The value of PicOrderCntVal shall be in the range of
−2^31 to 2^31 − 1, inclusive."

To match with these definitions change __u16 pic_order_cnt[2]
into __s32 pic_order_cnt_val.
Change v4l2_ctrl_hevc_slice_params->slice_pic_order_cnt to __s32 too.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@collabora.com>
Reviewed-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Acked-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Tested-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>