net: macb: Kconfig: Make MACB depend on COMMON_CLK

commit c218ad55 ("macb: Add support for SiFive FU540-C000") added a
dependency on the common clock framework to the macb driver, but didn't
express that dependency in Kconfig.  As a result macb now fails to
compile on systems without COMMON_CLK, which specifically causes a build
failure on powerpc allyesconfig.

This patch adds the dependency, which results in the macb driver no
longer being selectable on systems without the common clock framework.
All known systems that have this device already support the common clock
framework, so this should not cause trouble for any uses.  Supporting
both the FU540-C000 and systems without COMMON_CLK is quite ugly.

I've build tested this on powerpc allyesconfig and RISC-V defconfig
(which selects MACB), but I have not even booted the resulting kernels.

Fixes: c218ad55 ("macb: Add support for SiFive FU540-C000")
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>