ARM: dts: msm: update display_panel_avdd regulator type for Lahaina

Change the compatible string for the display_panel_avdd regulator
from "regulator-fixed" to "qti-regulator-fixed".  This ensures that
proxy-consumer properties of this regulator are properly handled
at runtime.

Change-Id: I5f58a0b72968df47503544950c55a785d1681d00