USB: Fix OHCI warning

This patch fixes a warning introduces by the split endian OHCI support
patch on platforms that don't have readl_be/writel_be variants (though
mostly harmless as those are called in an if (0) statement, but gcc
still warns).

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>