database/sql: fix example usage of Out

Fixes #22292

Change-Id: I016e5f2b8624a6ebaf11a693a0f6d94d7b0d3f92
Reviewed-on: https://go-review.googlesource.com/71550
Reviewed-by: Daniel Theophanes <[email protected]>

Author: Tim Cooper

src/database/sql/sql.go

@@ -285,7 +285,7 @@ type Scanner interface {
 // Example usage:
 //
 //   var outArg string
-//   _, err := db.ExecContext(ctx, "ProcName", sql.Named("Arg1", Out{Dest: &outArg}))
+//   _, err := db.ExecContext(ctx, "ProcName", sql.Named("Arg1", sql.Out{Dest: &outArg}))
 type Out struct {
 	_Named_Fields_Required struct{}