rt2x00: fix spelling mistake in various macros, UKNOWN -> UNKNOWN

Rename several macros that contain mispellings of UNKNOWN

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>