rfreezefs.c (partial_cleanup): Don't ignore the argument.

Previously, the function would always attempt to thaw all of the
filesystems, even if they hadn't all been frozen yet.  There's only a
problem if something actually goes wrong during freezing some
filesystem, and this probably isn't too disastrous, assuming that the
filesystems in question weren't already frozen (and are now unexpectedly
thawed), but it's not desirable.