[media] cx23885: fix format/crop handling

While testing the cx23885 driver with various TV standards I found
a number of bugs:

1) norm_maxw() returned 768 instead of 720 for PAL formats. This should
   always be 720, so drop this inline function and just always use 720.
2) cropcap() was missing, so the pixelaspect was never known and qv4l2 would
   scale the image incorrectly. Add cropcap support.
3) cx23885_set_tvnorm() should just return 0 if the same standard was
   set again. If another standard is set, then reset the width/height and
   call set_fmt for the subdevs.

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