[ARM] pxa: fix HSIO bus x24 multiplier for pxa3xx

The latest PXA3xx DM has enabled 312MHz for the HSS bus,
which allows x24 multiplier.

Signed-off-by: Marek Vasut <marek.vasut@gmail.com>
Signed-off-by: Eric Miao <eric.y.miao@gmail.com>