sync/atomic: comment for Uintptr.Or incorrectly describes return value [1.24 backport]

[gopherbot]

@prattmic requested issue #75607 to be considered for backport to the next 1.24 minor release.

@gopherbot Please backport to 1.24 and 1.25. This is a documentation fix for sync/atomic.(*Uintptr).Or.

[gopherbot]

Change https://go.dev/cl/706855 mentions this issue: [release-branch.go1.24] sync/atomic: correct Uintptr.Or return doc