[PATCH] serial: add missing depends on ARCH_ZYNQ

[Alexander Aring]

Hi Steffen,

now I figoure out that this is a bigger problem.

There are architecture which not use the COMMON_CLK framework and has it
own clock framework implementation (for me it was ARCH_AT91). Then the
build failed.

So now we could make a depends on !ARCH_AT91 in COMMON_CLK and a depends
on COMMON_CLK in DRIVER_SERIAL_CADENCE... but this is very ugly and
maybe the ARCH_AT91 get a COMMON_CLK framework...

Sorry for the noise.

- Alex