Staging: rtl8192u: Add select WEXT_PRIV to Kconfig to prevent build failure

Without WEXT_PRIV set the driver fails to build due to unknown fields in
the iw_handler_def struct.
Those fields are enclosed in WEXT_PRIV conditionals in the prototype
of iw_handler_def in include/net/iw_handler.h
Signed-off-by: Peter Huewe <peterhuewe@gmx.de>
Acked-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/rtl8192u/Kconfig

 config RTL8192U
 	tristate "RealTek RTL8192U Wireless LAN NIC driver"
 	depends on PCI && WLAN && USB
-	depends on WIRELESS_EXT
+	select WIRELESS_EXT
+	select WEXT_PRIV
 	default N
 	---help---