opkg_cmd: fix return of opkg compare-versions

opkg_cmd: fix return of opkg compare-versions

The implementation of opkg compare-version was simply returning the return value
of pkg_version_satisfied(), which returns a boolean.  This results in inverted
logic in that:

$ opkg compare-version 1.0 == 1.0 || echo different
different

That's clearly not right.  As nobody had noticed this before presumably nobody
was actually using this (likely either opkg-compare-version or
opkg-compare-versions.sh) just change the return value so it's correct.

Signed-off-by: Ross Burton <ross.burton@intel.com>