I'm not sure where the information came from, but I assumed
that doing cache-inhibited mappings for mmio regions was
sufficient.

It seems we also need the guarded bit set, like everyone
else, which is the default for ioremap.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Paul Mackerras <paulus@samba.org>