Neglects to free errors allocated by qmp_guest_fsfreeze_thaw().
Spotted by Coverity.

While there, drop the test whether return value is negative (it's
never true), and improve logging.
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NLuiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: NMichael Roth <mdroth@linux.vnet.ibm.com>