clk: sunxi: a10: Add CLK_AHB_GMAC

CLK_AHB_GMAC was suppose to be part of previous commit
"clk: sunxi: Implement A10 EMAC clocks" add it so-that
we can get rid of sunxi_set_gate warning on boot message.

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>