media: docs: vidioc-g-ext-ctrls.rst: Update p_s32 and p_s64 types

The pointer types of p_s32 and p_s64 in v4l2_ext_control has been
updated, match the change in documentation.
Signed-off-by: Daniel Lundberg Pedersen <dlp@qtec.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>