usb: USB hubs require host mode

USB hubs run in host mode not in gadget mode. Hence, compiling usb_hub.c
should not be selected by CONFIG_USB_GADGET.

Suggested-by: Marek Vasut <marex@denx.de>
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Marek Vasut <marex@denx.de>
diff --git a/common/Makefile b/common/Makefile
index 252e965..a50302d 100644
--- a/common/Makefile
+++ b/common/Makefile
@@ -24,7 +24,7 @@
 obj-$(CONFIG_PHYLIB) += miiphyutil.o
 
 obj-$(CONFIG_USB_HOST) += usb.o usb_hub.o
-obj-$(CONFIG_USB_GADGET) += usb.o usb_hub.o
+obj-$(CONFIG_USB_GADGET) += usb.o
 obj-$(CONFIG_USB_STORAGE) += usb_storage.o
 obj-$(CONFIG_USB_ONBOARD_HUB) += usb_onboard_hub.o