net: stmmac: fix build failure due to missing COMMON_CLK dependency

This patch fix the build failure on m68k;
drivers/net/ethernet/stmicro/stmmac/dwmac-ipq806x.o: In function `ipq806x_gmac_probe':
dwmac-ipq806x.c:(.text+0xda): undefined reference to `clk_set_rate'
drivers/net/ethernet/stmicro/stmmac/dwmac-rk.o: In function `rk_gmac_probe':
dwmac-rk.c:(.text+0x1e58): undefined reference to `clk_set_rate'
drivers/net/ethernet/stmicro/stmmac/dwmac-sti.o: In function `stid127_fix_retime_src':
dwmac-sti.c:(.text+0xd8): undefined reference to `clk_set_rate'
dwmac-sti.c:(.text+0x114): undefined reference to `clk_set_rate'
drivers/net/ethernet/stmicro/stmmac/dwmac-sti.o:dwmac-sti.c:(.text+0x12c): more undefined references to `clk_set_rate' follow
Lots of stmmac platform drivers need COMMON_CLK in their Kconfig depends.

Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Signed-off-by: David S. Miller <davem@davemloft.net>