qapi: Fix doc comment indentation again

In commit 26ec4e53 and similar commits we fixed the indentation
for doc comments in our qapi json files to follow a new stricter
standard for indentation, which permits only:
    @arg: description line 1
          description line 2

or:
    @arg:
    line 1
    line 2

but because the script updates that enforce this are not yet in the
tree we have had a steady trickle of subsequent changes which didn't
follow the new rules.

Fix the latest round of mis-indented doc comments.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20200925162316.21205-2-peter.maydell@linaro.org>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
[Updated for commit 4c437254 and a83e24ba]
Signed-off-by: Markus Armbruster <armbru@redhat.com>