fix broken link in PartialEq doc

PartialEq doc was attempting to link to [`Eq`] but instead we got a link
to `eq`. Disambiguate with "trait@Eq".

Author: ericseppanen

library/core/src/cmp.rs

@@ -29,7 +29,7 @@ use self::Ordering::*;
 ///
 /// This trait allows for partial equality, for types that do not have a full
 /// equivalence relation. For example, in floating point numbers `NaN != NaN`,
-/// so floating point types implement `PartialEq` but not [`Eq`].
+/// so floating point types implement `PartialEq` but not [`trait@Eq`].
 ///
 /// Formally, the equality must be (for all `a`, `b` and `c`):
 ///