monitor/hmp-cmds.c: Clean up hmp_dumpdtb printf

monitor/hmp-cmds.c: Clean up hmp_dumpdtb printf

In hmp_dumpdtb(), we print a message when the command succeeds.  This
message is missing the trailing \n, so the HMP command prompt is
printed immediately after it.  We also weren't capitalizing 'DTB', or
quoting the filename in the message.  Fix these nits.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20250206151214.2947842-2-peter.maydell@linaro.org