cmd/compile/internal/ssa: cleanup godocs

Add a blank line before the "package ssa" lines so the "autogenerated
don't edit" comments don't end up in godoc output.

Change-Id: I82bf90d52d426ce1a8e21483fc8f47b3689259c7
Reviewed-on: https://go-review.googlesource.com/20086
Reviewed-by: Keith Randall <khr@golang.org>
diff --git a/src/cmd/compile/internal/ssa/rewritegeneric.go b/src/cmd/compile/internal/ssa/rewritegeneric.go
index 0c71b2c..ad2abc5 100644
--- a/src/cmd/compile/internal/ssa/rewritegeneric.go
+++ b/src/cmd/compile/internal/ssa/rewritegeneric.go
@@ -1,5 +1,6 @@
 // autogenerated from gen/generic.rules: do not edit!
 // generated with: cd gen; go run *.go
+
 package ssa
 
 import "math"