TunerHAL Fix bug in TS Size Read

Previously in CL 19152256 the size variables for Pes and
Section event reading were made unsigned in order to
prevent negative values. However, the conversion from
int8_t directly to uint32_t still produces incorrect values.
To solve this, the values which are read in are first
converted from int8_t to uint8_t before their final
conversion.

Bug: 238797416
Test: Run on Cuttlefish with TS input, and view logging.
Old version should not work with any TS that declares a
size containing any byte with value > 0x80.

Change-Id: I55bb552bc857fd8acf16729f8cfcb9e147e07e9c