ARM: dts: omap4: Fix sgx clock rate for 4430

We currently have a different clock rate for droid4 compared to the
stock v3.0.8 based Android Linux kernel:

# cat /sys/kernel/debug/clk/dpll_*_m7x2_ck/clk_rate
266666667
307200000
# cat /sys/kernel/debug/clk/l3_gfx_cm:clk:0000:0/clk_rate
307200000

Let's fix this by configuring sgx to use 153.6 MHz instead of 307.2 MHz.
Looks like also at least duover needs this change to avoid hangs, so
let's apply it for all 4430.

This helps a bit with thermal issues that seem to be related to memory
corruption when using sgx. It seems that other driver related issues
still remain though.

Cc: Arthur Demchenkov <spinal.by@gmail.com>
Cc: Merlijn Wajer <merlijn@wizzup.org>
Cc: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>