[media] v4l2-ctrls: use ptrs for all but the s32 type

Rather than having two unions for all types just keep 'val' and
'cur.val' and use the p_cur and p_new unions to access all others.

The only reason for keeping 'val' and 'cur.val' is that it is used
all over, so converting this as well would be a huge job.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>