Fix mapped_index::find_name_components_bounds upper bound computation

Fix mapped_index::find_name_components_bounds upper bound computation

Here we want to find where we'd insert "after", so we want
std::lower_bound, not std::upper_bound.

gdb/ChangeLog:
2017-11-21  Pedro Alves  <palves@redhat.com>

	* dwarf2read.c (mapped_index::find_name_components_bounds)
	<completion mode, upper bound>: Use std::lower_bound instead of
	std::upper_bound.
	(test_mapped_index_find_name_component_bounds): Remove incorrect
	"t1_fund" from expected symbols.