Do not resolve associated const when there is no provided value

tests/ui/crashes/ice-6252.stderr

@@ -30,15 +30,7 @@ LL |     const VAL: T;
 LL | impl<N, M> TypeVal<usize> for Multiply<N, M> where N: TypeVal<VAL> {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ missing `VAL` in implementation
 
-error: constant expression depends on a generic parameter
-  --> $DIR/ice-6252.rs:13:9
-   |
-LL |     [1; <Multiply<Five, Five>>::VAL];
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: this may fail depending on what value the parameter takes
-
-error: aborting due to 4 previous errors
+error: aborting due to 3 previous errors
 
 Some errors have detailed explanations: E0046, E0412.
 For more information about an error, try `rustc --explain E0046`.