ipq40xx: fix art partition name WHW03 V1

ipq40xx: fix art partition name WHW03 V1

In the blamed commit, the wrong partition name for ART was used.

It was later discovered that the partition table uses "0:ART" instead of
"art" for the ART partition name thus breaking caldata extraction.

So, fix the partition name.

Fixes: 274f6e5ab849 ("treewide: linksys: use nvmem MAC for hw_mac_addr")
Signed-off-by: Anthony Sepa <protectivedad@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/22596
Signed-off-by: Robert Marko <robimarko@gmail.com>