iter: fix a tiny doc comment bug

Use the right name for method Pos.Value in a sample doc comment in the package overview.

Fixes #76187.

Change-Id: Id1f5b0ca4ea39493b10140bc304c57c081c805ee
GitHub-Last-Rev: 7bf5d07
GitHub-Pull-Request: #76195
Reviewed-on: https://go-review.googlesource.com/c/go/+/718321
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Alan Donovan <adonovan@google.com>
Auto-Submit: Alan Donovan <adonovan@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

Author: bobg

src/iter/iter.go

@@ -188,7 +188,7 @@ For example, a tree implementation might provide:
 	// It is only valid during the yield call it is passed to.
 	type Pos[V any] struct { ... }
 
-	// Pos returns the value at the cursor.
+	// Value returns the value at the cursor.
 	func (p *Pos[V]) Value() V
 
 	// Delete deletes the value at this point in the iteration.