cdrom: add missing BCD->int convert in cdrFreeze()

For some Eboot .PBP game images, when loading a savestate, a zlib error
like 'uncompress failed with -5 for block 5383, sector 86132' would be
output to stdout/stderr. The savestate would still be playable, though.

Traced it down to cdrFreeze() failing to convert cdr.Prev from BCD->int
when calling ReadTrack(). Note that the odd 'cdr.Prev[0]++;' line seems
to be someone's hacky way of forcing ReadTrack() to avoid skipping what
it thinks is a duplicate sector read.