ARM: pxa: define clock registers as __iomem

We should not dereference registers as pointers, so use readl/writel
instead for these registers.

The clock registers are accessed in multiple files, so we have to
change them all at once.

I stumbled over these registers while looking at something unrelated.
There are in fact other registers with the same problem, but I did
not try to address those at this point.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>