Let's fix pinmux address of gpio 170 used by tfp410 powerdown-gpio.

According to the OMAP35x Technical Reference Manual
  CONTROL_PADCONF_I2C3_SDA[15:0]  0x480021C4 mode0: i2c3_sda
  CONTROL_PADCONF_I2C3_SDA[31:16] 0x480021C4 mode4: gpio_170
the pinmux address of gpio 170 must be 0x480021C6.

The former wrong address broke i2c3 (used by hdmi ddc), resulting in
kernel message:
  omap_i2c 48060000.i2c: controller timed out

Fixes: 8cecf52b ("ARM: omap3-beagle.dts: add display information")
Cc: stable@vger.kernel.org # v3.15+
Signed-off-by: Carl Frederik Werner <frederik@cfbw.eu>
Signed-off-by: Tony Lindgren <tony@atomide.com>