Use "bzip2" instead of "bzip" in optparse's compression choices for the
convert command. This is both more accurate and matches what the
ParseCompressionTypeString function expects.
The mismatch between the two parsing functions prevented compression
using bzip2 because either ParseCompressionTypeString or optparse would
generate an error when using "bzip" or "bzip2" respectively.
Fixes https://bugs.dolphin-emu.org/issues/13427
a1d6a54eaa