USB: s3c2410: deactivate endpoints before gadget unbinding

Gadget disconnect must be called before unbinding to avoid races.
The change fixes an oops on g_ether module unregistering.

Signed-off-by: Vladimir Zapolskiy <vzapolskiy@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>