media: dvb-frontends: tda10048: Fix integer overflow

state->xtal_hz can be up to 16M, so it can overflow a 32 bit integer
when multiplied by pll_mfactor.

Create a new 64 bit variable to hold the calculations.

Link: https://lore.kernel.org/linux-media/20240429-fix-cocci-v3-25-3c4865f5a4b0@chromium.org
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>