Ha, okay, figured it out. The second set of instructions on the wiki page have a longer boot_openwrt U-Boot var, with multiple attempts to resize the fdt:
setenv boot_openwrt "cp.b 0xEC000000 0x2000000 0x2000000; interrupts off; bootm start 0x2000000; bootm loados; fdt resize; fdt boardsetup; fdt resize; fdt boardsetup; fdt chosen; fdt resize; fdt chosen; bootm prep; bootm go;"
versus the step-by-step version, which doesn't work:
setenv boot_openwrt "cp.b 0xEC000000 0x2000000 0x2000000; interrupts off; bootm start 0x2000000; bootm loados; fdt resize; fdt boardsetup; fdt chosen; bootm prep; bootm go;"
Used the longer version, and saveenv again, and booted first try.