usb: phy: fix Kconfig warning

Recent commits introduced the following
Kconfig warning:

warning: (USB_MUSB_HDRC && OMAP_USB3) selects \
	OMAP_CONTROL_USB which has unmet direct \
	dependencies (USB_SUPPORT && ARCH_OMAP2PLUS)

This patch just fixes it, by removing the
unnecessary OMAP dependency.

Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>