clk: ti: dra7: fix parent for gmac_clkctrl

The parent clk for gmac clk ctrl has to be gmac_main_clk (125MHz) instead
of dpll_gmac_ck (1GHz). This is caused incorrect CPSW MDIO operation.
Hence, fix it.

Fixes: dffa9051 ('clk: ti: dra7: add new clkctrl data')
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Tero Kristo <t-kristo@ti.com>