dwarf2.c: simplify best_fit_len tests

	* dwarf2.c (lookup_address_in_function_table): Simplify
	best_fit_len test.
	(info_hash_lookup_funcinfo): Likewise.
	(lookup_symbol_in_function_table): Likewise, also reorder tests
	and check "file" is set.
	(lookup_symbol_in_variable_table): Reorder tests.