media: videodev2.h: Fix p_s32 and p_s64 pointer types

Use the intended pointer types for p_s32 and p_64 in the union of the
struct v4l2_ext_control.

Fixes: e77eb663 ("videodev2.h: add p_s32 and p_s64 pointers")
Signed-off-by: Daniel Lundberg Pedersen <dlp@qtec.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>