V4L/DVB (12485): zl10353: correct implementation of FE_READ_UNCORRECTED_BLOCKS

Makes zl10353 a bit more DVB API compliant:
FE_READ_UNCORRECTED_BLOCKS - keep a counter of UNC blocks
FE_GET_FRONTEND - return last set frequency instead of zero

Signed-off-by: Aleksandr V. Piskunov <alexandr.v.piskunov@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>