[ARM] 3984/1: ixp4xx/nslu2: Fix disk LED numbering (take 2)

This patch fixes an error in the numbering of the disk LEDs on the
Linksys NSLU2. The error crept in because the physical location
of the LEDs has the Disk 2 LED *above* the Disk 1 LED.

Thanks to Gordon Farquharson for reporting this.

Signed-off-by: Rod Whitby <rod@whitby.id.au>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>