V4L/DVB (4868): Dvb-pll: return frequency set by dvb_pll_configure()

This patch removes some duplicated code by returning the frequency set by
dvb_pll_configure(), instead of recalculating it again in dvb_pll_set_params()
and dvb_pll_calc_regs().
If the return value of dvb_pll_configure is less than zero, it is an error
code.  Otherwise, the return value is the frequency actually set by the
function.

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