usb: eth: fix Makefile

fix obj-y term

Signed-off-by: Rene Griessl <rgriessl@cit-ec.uni-bielefeld.de>
diff --git a/drivers/usb/eth/Makefile b/drivers/usb/eth/Makefile
index 94551c4..e6ae9f1 100644
--- a/drivers/usb/eth/Makefile
+++ b/drivers/usb/eth/Makefile
@@ -5,8 +5,6 @@
 
 # new USB host ethernet layer dependencies
 obj-$(CONFIG_USB_HOST_ETHER) += usb_ether.o
-ifdef CONFIG_USB_ETHER_ASIX
-obj-y += asix.o
-endif
+obj-$(CONFIG_USB_ETHER_ASIX) += asix.o
 obj-$(CONFIG_USB_ETHER_MCS7830) += mcs7830.o
 obj-$(CONFIG_USB_ETHER_SMSC95XX) += smsc95xx.o