usb: msm_otg: Vote for EXT_3P3V regulator for MHL connector

In case of 8960 Liquid, need to vote for EXT_3P3V regulator
to avoid usb connection lost as MHL analog switch is powered
by this regulator.

Change-Id: Ifc36d7916a5407801fdf43357176efa264d160bd
CRs-fixed: 315979
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>