rt2400pci: fix RSSI read

commit 2bf127a5cc372b9319afcbae10b090663b621c8b upstream.

RSSI value is provided on word3 not on word2.

Signed-off-by: Stanislaw Gruszka <stf_xl@wp.pl>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>