ARM: dts: Use LPG4 for dsi panel backlight control on 8974 pro AC

The dsi panel's backlight control is driven by the output of LPG channel
4. Update the 8974 Pro AC deive tree file to reflect that.

Change-Id: I64b325ef94ffcbc208a692f3ed1f27ac46e23f71
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>
Signed-off-by: Jeevan Shriram <jshriram@codeaurora.org>
1 file changed