device_tree: Replace error_setg(&error_fatal) by error_report() + exit()

device_tree: Replace error_setg(&error_fatal) by error_report() + exit()

Use error_report() + exit() instead of error_setg(&error_fatal),
as suggested by the "qapi/error.h" documentation:

   Please don't error_setg(&error_fatal, ...), use error_report() and
   exit(), because that's more obvious.

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Message-id: 20180625165749.3910-4-f4bug@amsat.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>