cmd/protoc-gen-go: update deprecation warning

Change-Id: Ie1a854bf6f47d4ca9e941b6ccc64dc24ff32bd19
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/186657
Reviewed-by: Damien Neil <dneil@google.com>
diff --git a/internal/testprotos/irregular/test.pb.go b/internal/testprotos/irregular/test.pb.go
index c3985ce..f25f971 100644
--- a/internal/testprotos/irregular/test.pb.go
+++ b/internal/testprotos/irregular/test.pb.go
@@ -52,7 +52,7 @@
 	return mi.MessageOf(x)
 }
 
-// Deprecated: Use Message.ProtoReflect.Type instead.
+// Deprecated: Use Message.ProtoReflect.Descriptor instead.
 func (*Message) Descriptor() ([]byte, []int) {
 	return file_irregular_test_proto_rawDescGZIP(), []int{0}
 }