net: switchdev: use obj-$(CONFIG_NET_SWITCHDEV) form in net/Makefile

CONFIG_NET_SWITCHDEV is a bool option. Change the ifeq conditional to
the standard obj-$(CONFIG_NET_SWITCHDEV) form.

Use obj-y in net/switchdev/Makefile because Kbuild visits this Makefile
only when CONFIG_NET_SWITCHDEV=y.
Signed-off-by: NMasahiro Yamada <masahiroy@kernel.org>
Link: https://lore.kernel.org/r/20210125231659.106201-3-masahiroy@kernel.orgSigned-off-by: NJakub Kicinski <kuba@kernel.org>

net/Makefile

@@ -72,9 +72,7 @@ obj-$(CONFIG_VSOCKETS)	+= vmw_vsock/
 obj-$(CONFIG_MPLS)		+= mpls/
 obj-$(CONFIG_NET_NSH)		+= nsh/
 obj-$(CONFIG_HSR)		+= hsr/
-ifneq ($(CONFIG_NET_SWITCHDEV),)
-obj-y				+= switchdev/
-endif
+obj-$(CONFIG_NET_SWITCHDEV)	+= switchdev/
 ifneq ($(CONFIG_NET_L3_MASTER_DEV),)
 obj-y				+= l3mdev/
 endif

net/switchdev/Makefile

@@ -3,4 +3,4 @@
 # Makefile for the Switch device API
 #
 
-obj-$(CONFIG_NET_SWITCHDEV) += switchdev.o
+obj-y += switchdev.o