usb: cdc-wdm: Fix race between write and disconnect

Unify mutexes to fix a race between write and disconnect
and shift the test for disconnection to always report it.

Signed-off-by: Oliver Neukum <neukum@b1-systems.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 file changed