Re: dtc: Generate useful error message for properties after subnodes

So, like, the other day David Gibson mumbled:

On several occasions, I've accidentally put properties after subnodes
in a dts file.  I've then spent ages thinking that the resulting
syntax error was because of something else.

This patch arranges for this specific syntax error to generate a more
specific and useful error message.

Signed-off-by: David Gibson <redacted>

Applied.

jdl