[media] v4l2-ioctl.c: fix inverted condition

v4l_print_ext_controls() would print the 'size' if it was 0 and
'value' if size was non-zero, but it should have been the other
way around.

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