[PATCH] USB gadgetfs: fixes an error on writing to endpoint file

this patch fixes an "Invalid argument" error returned by a write to an
endpoint-file after reopening it in the gadgetfs module in the kernel
2.6.12.

This was testet only with dummy_hcd module!

Signed-off-by: Pavol Kurina <kurina@gmx.net>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>