bzip2: fixup build after ea448fef (convert to gentargets, add host package, bump version)

Fix a few typos/mistakes introduced in commit ea448fef:

- bzip2 soname is not the same as package version
- It is PKG_INSTALL_STAGING, not PKG_STAGING_INSTALL
- Typo: BZIP2_INSTALL_TARGET_CMDS, not B2IP_INSTALL_TARGET_CMDS

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>