usb: msm_otg: Update DT documentation for vbus_otg supply

vbus_otg is optional property that can be used to supply
VBUS in USB host mode.

Change-Id: I27b0ac0dbba909ae356c3133fbf4f8a76b9ae57d
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>
1 file changed