ARM: dts: at91: sama5d27_som1_ek: fix USB host vbus

The USB host has 3 ports so we must specify the entries for each
in the atmel,vbus-gpio property.
The specified pin (PA27) is the vbus for USBB and not USBA.

Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>
[claudiu.beznea@microchip.com: change subject to match the desired prefix]
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>