rtl8192u uses usb_* interfaces so it should depend on USB.
ERROR: "usb_kill_urb" [drivers/staging/rtl8192u/r8192u_usb.ko] undefined!
ERROR: "usb_deregister" [drivers/staging/rtl8192u/r8192u_usb.ko] undefined!
ERROR: "usb_control_msg" [drivers/staging/rtl8192u/r8192u_usb.ko] undefined!
ERROR: "usb_submit_urb" [drivers/staging/rtl8192u/r8192u_usb.ko] undefined!
ERROR: "usb_register_driver" [drivers/staging/rtl8192u/r8192u_usb.ko] undefined!
ERROR: "usb_free_urb" [drivers/staging/rtl8192u/r8192u_usb.ko] undefined!
ERROR: "usb_alloc_urb" [drivers/staging/rtl8192u/r8192u_usb.ko] undefined!
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
 config RTL8192U
        tristate "RealTek RTL8192U Wireless LAN NIC driver"
-       depends on PCI && WLAN
+       depends on PCI && WLAN && USB
        depends on WIRELESS_EXT
        default N
        ---help---