x86/PCI: Replace deprecated EXTRA_CFLAGS with ccflags-y

Update arch/x86/pci/Makefile replacing the deprecated EXTRA_CFLAGS with the
ccflags-y matching recommendation per section 3.7 of
Documentation/kbuild/makefiles.txt.

Link: https://lore.kernel.org/r/20190819060532.17093-1-kw@linux.comSigned-off-by: NKrzysztof Wilczynski <kw@linux.com>
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>

arch/x86/pci/Makefile

@@ -24,6 +24,4 @@ obj-y				+= bus_numa.o
 obj-$(CONFIG_AMD_NB)		+= amd_bus.o
 obj-$(CONFIG_PCI_CNB20LE_QUIRK)	+= broadcom_bus.o
 
-ifeq ($(CONFIG_PCI_DEBUG),y)
-EXTRA_CFLAGS += -DDEBUG
-endif
+ccflags-$(CONFIG_PCI_DEBUG)	+= -DDEBUG