dt-bindings: marvell,pxa168: add clock id for SDH3

There are four SDHC peripherals on the PXA168, but only three of them
were present in the DT bindings. This commit adds the fourth.

Signed-off-by: Doug Brown <doug@schmorgal.com>
Link: https://lore.kernel.org/r/20220612192937.162952-10-doug@schmorgal.com


Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>