ar71xx has just one board name "wndr3700" for WNDR3700 V1/V2, WNDR3800 and WNDR3800CH, whereas ath79 provides separate images for the boards. So, update SUPPORTED_DEVICES to store the correct ar71xx board names. Fixes: FS#2510 Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>