diagnostics: avoid querying associated_item in the resolver

Fixes #108529

tests/ui/resolve/issue-108529.rs

@@ -0,0 +1,8 @@
+#![allow(nonstandard_style)]
+use f::f::f; //~ ERROR
+
+trait f {
+    extern "C" fn f();
+}
+
+fn main() {}

tests/ui/resolve/issue-108529.stderr

@@ -0,0 +1,9 @@
+error[E0432]: unresolved import `f::f`
+  --> $DIR/issue-108529.rs:2:8
+   |
+LL | use f::f::f;
+   |        ^ expected type, found associated function `f` in `f`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0432`.