V4L/DVB (3889): Sort out support for non-attached tuners on mt352

Make it use set_params/pllbuf as appropriate so it works with
dvb_pll_attach()ed tuners.

Signed-off-by: Andrew de Quincey <adq_dvb@lidskialf.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>