USB: phy: remove CONFIG_USB_DEBUG usage

Now that no USB phy driver is using CONFIG_USB_DEBUG, remove it from the
Makefile.
Acked-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/phy/Makefile

 #
 # Makefile for physical layer USB drivers
 #
-
-ccflags-$(CONFIG_USB_DEBUG) := -DDEBUG
-
 obj-$(CONFIG_USB_PHY)			+= phy.o
 obj-$(CONFIG_OF)			+= of.o