USB: goku_udc: Remove crude cache coherency code

This is deep architecture specific magic and does should not to exist
in a driver.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Cc: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>