msm_fb: display: Set HDMI PLL footswitch regulator to 1.8V after get()

After regulator_get call for HDMI PLL footswitch purpose, set
output voltage to 1.8 V to ensure proper state while enabling and
disabling regulator.

Signed-off-by: Ravishangar Kalyanam <rkalya@codeaurora.org>
Change-Id: Ifdd0cdbf614524b53038074b943cca65b71bbd24