Fix cast of xml_find_attribute's return value

Fix cast of xml_find_attribute's return value

The cast auto-insert script inserted long unsigned int, but we should
use the typedef ULONGEST.  Fixes build failures on i386.

gdb/ChangeLog:

	* btrace.c (parse_xml_btrace_block): Fix cast of
	xml_find_attribute's return value.
	* memory-map.c (memory_map_start_memory): Likewise.
	* solib-svr4.c (library_list_start_library): Likewise.
	* solib-target.c (library_list_start_segment): Likewise.
	(library_list_start_section): Likewise.
	* tracepoint.c (traceframe_info_start_memory): Likewise.