USB gadget: gadgetfs dont try to lock before free

I spotted this during my tests with -rt on arm. The -rt patch contains
some better tools
to diagnose problems with locks and some other things...

Original code tries to take semaphore in BUG_ON and then free the memory
with this semaphore.

Signed-off-by: Milan Svoboda <msvoboda@ra.rockwell.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>