go/ssa: incorrect document in type Builtin struct

There is no Func field in CallCommon. s/CallCommon.Func/CallCommon.Value/ in the documentation for Builtin.

Fixes #46972

Change-Id: I501e9439bc0b1cb4f1dac0582f27e74de67e61b9
GitHub-Last-Rev: 6f07a2c80253c628b31970a2b1774644d93b3920
GitHub-Pull-Request: golang/tools#327
Reviewed-on: https://go-review.googlesource.com/c/tools/+/331310
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Tim King <taking@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Tim King <taking@google.com>
diff --git a/go/ssa/ssa.go b/go/ssa/ssa.go
index c604272..d3faf44 100644
--- a/go/ssa/ssa.go
+++ b/go/ssa/ssa.go
@@ -437,7 +437,7 @@
 // A Builtin represents a specific use of a built-in function, e.g. len.
 //
 // Builtins are immutable values.  Builtins do not have addresses.
-// Builtins can only appear in CallCommon.Func.
+// Builtins can only appear in CallCommon.Value.
 //
 // Name() indicates the function: one of the built-in functions from the
 // Go spec (excluding "make" and "new") or one of these ssa-defined