binder: fix PartialEq impl of SpIBinder

It was inconsistent with the definition of PartialOrd, which uses
`AIBinder_lt/gt` and has different behavior.

Test: m
Change-Id: I67e779a070c7b742be7c91ce52e43253f72d8db4
diff --git a/libs/binder/rust/src/proxy.rs b/libs/binder/rust/src/proxy.rs
index 340014a..04f1517 100644
--- a/libs/binder/rust/src/proxy.rs
+++ b/libs/binder/rust/src/proxy.rs
@@ -195,7 +195,7 @@
 
 impl PartialEq for SpIBinder {
     fn eq(&self, other: &Self) -> bool {
-        ptr::eq(self.0.as_ptr(), other.0.as_ptr())
+        self.cmp(other) == Ordering::Equal
     }
 }