ARM: davinci: omapl138-hawk: add missing regulator constraints for OHCI

We need to enable status changes for the fixed power supply for the USB
controller.

Fixes: 1d272894 ("ARM: davinci: omapl138-hawk: add a fixed regulator for ohci-da8xx")
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>