fdtdump: Fix over-zealous version check

It's perfectly valid for a dtb to have version and last compat version set
to the same value, and that value can be 17 (the latest defined version).
However, since 0931cea3 "dtc: fdtdump: check fdt if not in scanning mode"
fdtdump will refuse to process such a dtb.  We get away with this in many
cases because dtc's typical output has last compat version equal to 16,
rather than 17, but it's still a bug.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>