Staging: rt2860: remove dependency on WIRELESS_EXT version

As the driver is in mainline now we can remove such dependencies.
WIRELESS_EXT is 22 now.

Signed-off-by: Alexander Beregalov <a.beregalov@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>