ARM: dts: dra7: Change pbias voltage to 3.3V

As per recent TRM[1], PBIAS cell on dra7 devices supports
3.3v and not 3.0v as documented earlier.

Update PBIAS regulator max voltage and the voltage written
in the driver to reflect this.

[1] http://www.ti.com/lit/pdf/sprui30



Signed-off-by: Faiz Abbas <faiz_abbas@ti.com>