[media] em28xx: Fix height setting on non-progressive captures

This was introduced on commit c2a6b54a9:
"em28xx: fix: don't do image interlacing on webcams"

The proposed patch by Ezequiel is wrong. The right fix here is to just
don't bother here if either the image is progressive or not.

Reported-by: Ezequiel Garcia <elezegarcia@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>