ARM: 7596/1: mmci: replace readsl/writesl with ioread32_rep/iowrite32_rep

Not all the architectures have readsl/writesl,
use the more portable ioread32_rep/iowrite32_rep functions instead.

Signed-off-by: Davide Ciminaghi <ciminaghi@gnudd.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>