apm821xx: dts: explicitly set the partition reg size for Netgear WNDR4700

apm821xx: dts: explicitly set the partition reg size for Netgear WNDR4700

Correct the mtd partition reg property size to address the following
dtc warnings:

../dts/netgear-wndr4700.dts:191.6-33: Warning (reg_format): /plb/opb/ebc/ndfc@1,0/nand/partitions/partition@0/partition@40000:reg: property has invalid length (8 bytes) (#address-cells == 2, #size-cells == 1)

Signed-off-by: Shiji Yang <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/18242
Signed-off-by: Hauke Mehrtens <[email protected]>