sync/atomic: correct Uintptr.Or return doc

Uintptr.Or returns the old value, just like all of the other Or
functions. This was a typo in the original CL 544455.

Fixes #75607.

Change-Id: I260959e7e32e51f1152b5271df6cc51adfa02a4d
Reviewed-on: https://go-review.googlesource.com/c/go/+/706816
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Mauri de Souza Meneguzzo <mauri870@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Michael Pratt <mpratt@google.com>

Author: prattmic

src/sync/atomic/type.go

@@ -232,7 +232,7 @@ func (x *Uintptr) Add(delta uintptr) (new uintptr) { return AddUintptr(&x.v, del
 func (x *Uintptr) And(mask uintptr) (old uintptr) { return AndUintptr(&x.v, mask) }
 
 // Or atomically performs a bitwise OR operation on x using the bitmask
-// provided as mask and returns the updated value after the OR operation.
+// provided as mask and returns the old value.
 func (x *Uintptr) Or(mask uintptr) (old uintptr) { return OrUintptr(&x.v, mask) }
 
 // noCopy may be added to structs which must not be copied