usb: Remove OHCI useless masking/unmasking of WDH interrupt

The OHCI driver's IRQ handler, while processing a WDH interrupt, masks
and unmasks it.  I believe this is both broken (the write may still be
posted during the donelist processing it's trying to safeguard) and
useless as this IRQ may not be reissued until it's acked (unless this
legacy code is an uncommented workaround for some chip erratum).

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>