man: fix formatting of macros in sd_bus_add_object

man: fix formatting of macros in sd_bus_add_object

docbook would convert the newline to a space before the first argument:
  SD_BUS_METHOD_WITH_ARGS( member, args, result, handler)

And we need each item in a separate <para>, otherwise they'll all be in
one line.

(cherry picked from commit 3c080282e928a7edfcdb74feb2139ef1ac6f2ad0)