[media] dvb-frontends/stv0367dd: code refactoring and fixups

Fixup some minors and refactor code parts (e.g. statistics inquiry, DVBv5):
- get rid of unneeded omode enum and it's values, use fe_delivery_system
  values for this purpose
- make use of FE_* enums instead of raw hex values in read_status()
- define pr_fmt, remove module name from existing pr_* calls and improve
  verbosity
- refactor i2c read transfer into separate function, report read errors
- use errno defines for error reporting
- drop Log10x100() and utilise intlog10() from dvb_math for SNR math
- refactor read_* inquiry into DVBv5 and get_frontend(), slightly refactor
  snr inquiry