clk: ti: am43xx: Fix clock parent for RTC clock

Currently enabling clkctrl clock on am4 can fail for RTC as the clock
parent is wrong for RTC.

Fixes: 76a1049b

 ("clk: ti: am43xx: add new clkctrl data for am43xx")
Signed-off-by: Tony Lindgren <tony@atomide.com>
Link: https://lkml.kernel.org/r/20200221171030.39326-1-tony@atomide.com
Acked-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>