Staging: prism2-usb: Build should select WIRELESS_EXT

The prevailing idiom is to select WIRELESS_EXT not depend on it.

Depending leaves this driver in a situation where it can only
be built if another driver that selects WIRELESS_EXT has been enabled.
Signed-off-by: NSimon Horman <horms@verge.net.au>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/staging/wlan-ng/Kconfig

 config PRISM2_USB
 	tristate "Prism2.5/3 USB driver"
-	depends on WLAN && USB && WIRELESS_EXT
+	depends on WLAN && USB
+	select WIRELESS_EXT
 	default n
 	---help---
 	  This is the wlan-ng prism 2.5/3 USB driver for a wide range of