usb: phy: omap: get rid of omap_get_control_dev()

This function was preventing us from supporting multiple
instances. Get rid of it. Since we support DT boots only,
users can get the control device phandle from the DT node.

Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>