gccrs: Simplify crate number lookup

Uses the hir mapping getter instead of directly using the set.

gcc/rust/ChangeLog:

	* util/rust-hir-map.cc (Mappings::get_ast_crate_by_node_id_raw): Use
	appropriate getter.

Signed-off-by: Pierre-Emmanuel Patry <pierre.emmanuel.patry@opensrcsec.com>
1 file changed