ARM: keystone: Avoid calling of_clk_init() twice

With commit 4178bac4 {ARM: call of_clk_init from default time_init
handler}, of_clk_init() is always called on machines using default
time_init handler.

So drop the of_clk_init() from keystone code to avoid below
boot errors because of double call.

_of_pll_clk_init: error initializing pll mainpllclk
_of_pll_clk_init: error initializing pll papllclk
_of_pll_clk_init: error initializing pll ddr3apllclk
_of_pll_clk_init: error initializing pll ddr3bpllclk
_of_pll_clk_init: error initializing pll armpllclk

Reported-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>