usb/dev-mtp: Fix Error double free after inotify failure

usb/dev-mtp: Fix Error double free after inotify failure

error_report_err() frees its first argument.  Freeing it again is
wrong.  Don't.

Fixes: 47287c27d0c367a89f7b2851e23a7f8b2d499dd6
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Daniel P. Berrangé <berrange@redhat.com>
Cc: qemu-stable@nongnu.org
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20200630090351.1247703-7-armbru@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
(cherry picked from commit 562a558647be6fe43e60f8bf3601e5b6122c0599)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>