fdt: fix incorrect placement of partition information for atmel_nand

fdt: fix incorrect placement of partition information for atmel_nand

fdt_node_set_part_info() blindly assumes, that the first child of the
given node must be the 'partitions' node where to put the part info.
In case of atmel_nand this node is actually the NFC node.

Use the Linux kernel logic skipping any node that has a 'compatible'
property prevent adding the partitions to a wrong node or deleting the
wrong parent node.