usb: dwc2: pci: Correctly compile dwc2-pci as a module or built-in

The dwc2-pci driver should be compiled as a module when configured to
do so. If the dwc2-pci is configured as a module but actually
built-in, it can cause build errors due to the fact that the
generic-phy will be allowed to compile as a module causing undefined
references.
Reported-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/dwc2/Makefile

@@ -19,10 +19,8 @@ endif
 # mode. The PCI bus interface module will called dwc2_pci.ko and the platform
 # interface module will be called dwc2_platform.ko.
 
-ifneq ($(CONFIG_USB_DWC2_PCI),)
-	obj-$(CONFIG_USB_DWC2)		+= dwc2_pci.o
-	dwc2_pci-y			:= pci.o
-endif
+obj-$(CONFIG_USB_DWC2_PCI)		+= dwc2_pci.o
+dwc2_pci-y				:= pci.o
 
 obj-$(CONFIG_USB_DWC2_PLATFORM)		+= dwc2_platform.o
 dwc2_platform-y				:= platform.o