media: dvb-frontends/stv0910: cast the BER denominator shift exp to ULL

To avoid miscalculations related to the BER denominator, the shift
expression needs to be casted as ULL.

Picked up from the upstream dddvb GIT.

Signed-off-by: Daniel Scheller <d.scheller@gmx.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>