clk: spear3xx: Set proper clock parent of uart1/2

The uarts only work when the parent is ras_ahb_clk. The stale 3.5
based ST tree does this in the board file.

Add it to the clk init function. Not pretty, but the mess there is
amazing anyway.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Mike Turquette <mturquette@linaro.org>