usb: cdc-acm: bugfix release()

Bugfixes to the usb_driver_release_interface() usage;

  (a) make sure releasing *either* interface first will release
      the other, instead of insisting it be the control interface;

  (b) remove the recently-added self-deadlock.

(The "fix disconnect bug in cdc-acm" patch was incomplete and incorrect.)

Plus a small "sparse" fix:  rename a local variable so it doesn't
shadow a function parameter.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Acked-by: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>