ramips: fix partition offset for D-Link DIR-810L

ramips: fix partition offset for D-Link DIR-810L

The Jffs2 partition for the D-Link DIR-810L is currently off by
0x10000. Apply the correct offset based on the other partitions'
size/offset and the information about stock OS from the Wiki.

This is just based on the named information and _not_ verified
on device.

Fixes: 36e3424fa520 ("ramips: add support for dir810l and asus rp-n53")

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
Tested-by: Roger Pueyo Centelles <roger.pueyo@guifi.net>