USB: usb_gadget.h whitespace fixes

This just fixes some whitespace bugs in <linux/usb_gadget.h>,
mostly extraneous spaces where a single tab suffices.
Signed-off-by: NDavid Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>