Minor changes in ada-tasks.c

Minor changes in ada-tasks.c

Just some minor cleanup changes in preparation for an upcoming
change...

gdb/ChangeLog  (Tristan Gingold)

	* ada-tasks.c: Renames fieldno to actb_fieldno.
	(ada_get_task_number): Indentation.
	(get_tcb_types_info): Remove all parameters.  Write directly
	the globals.
	(ptid_from_atcb_common): Adjust.
	(read_atcb): Adjust.