ARM: OMAP2+: Fix warnings with broken omap2_set_init_voltage()

[ Upstream commit cf395f7d ]

This code is currently unable to find the dts opp tables as ti-cpufreq
needs to set them up first based on speed binning.

We stopped initializing the opp tables with platform code years ago for
device tree based booting with commit 92d51856 ("ARM: OMAP3+: do not
register non-dt OPP tables for device tree boot"), and all of mach-omap2
is now booting using device tree.

We currently get the following errors on init:

omap2_set_init_voltage: unable to find boot up OPP for vdd_mpu
omap2_set_init_voltage: unable to set vdd_mpu
omap2_set_init_voltage: unable to find boot up OPP for vdd_core
omap2_set_init_voltage: unable to set vdd_core
omap2_set_init_voltage: unable to find boot up OPP for vdd_iva
omap2_set_init_voltage: unable to set vdd_iva

Let's just drop the unused code. Nowadays ti-cpufreq should be used to
to initialize things properly.

Cc: Adam Ford <aford173@gmail.com>
Cc: André Roth <neolynx@gmail.com>
Cc: "H. Nikolaus Schaller" <hns@goldelico.com>
Cc: Nishanth Menon <nm@ti.com>
Cc: Tero Kristo <t-kristo@ti.com>
Tested-by: Adam Ford <aford173@gmail.com> #logicpd-torpedo-37xx-devkit
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>