net/nuc900: enable Mac driver clock

This patch fixed a bug that Mac driver does not work,because I missed the clk enable.

I have ever tested the driver when I submitted previous Mac driver patch,
and it worked good, since my bootloader has enabled the clock in advance.

But when I try to use other bootloader where clock engine was disabled,the
Mac driver does not work, so I send this patch to fix this issue.

Signed-off-by: Wan ZongShun <mcuos.com@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>