dt-bindings: ata: Convert arasan,cf-spear1340 to DT schema

Convert the Arasan/SPEAr Compact Flash Controller to DT schema format.

The "clock-frequency" property isn't actually used. Add a single
"clocks" entry as the Linux driver supports a single clock though the
platform still doesn't have clocks in DT.

Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>