V4L/DVB (7597): em28xx: share the same xc3028 setup for analog and digital modes

Thanks to Devin Heitmueller <devin.heitmueller@gmail.com> and Aidan
Thornton" <makosoft@googlemail.com> for pointing some errors with the
previous scenario.

Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>