ARM: dts: i.MX51: digi-connectcore-som: Setup usbotg vbus-supply

The VBUS on usbotg is connected to the PMIC SWBST, let's reflect
that in the bindings.

Signed-off-by: Alexander Shiyan <[e-mail]>
Signed-off-by: Shawn Guo <[e-mail]>

arch/arm/boot/dts/imx51-digi-connectcore-som.dtsi

···
 &usbotg {
 	phy_type = "utmi_wide";
 	disable-over-current;
+	vbus-supply = <&swbst_reg>;
 	/* Device role is not known, keep status disabled */
 };