USB: uas: fix locking

Forgot to unlock in the uas_eh_task_mgmt error paths.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>