Add missing linking regulator node to usb bus for power usb devices.

Cc: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Cc: Jerome Brunet <jbrunet@baylibre.com>
Cc: Neil Armstrong <narmstrong@baylibre.com>
Acked-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Anand Moon <linux.amoon@gmail.com>
[ khilman: minor typo fixup ]
Signed-off-by: Kevin Hilman <khilman@baylibre.com>