[dev.ssa] cmd/compile: fix test verb

The verb doesn't do anything, but if/when we move
these to the test directory, having it be right
will be one fewer thing to remember.

Change-Id: Ibf0280d7cc14bf48927e25215de6b91c111983d9
Reviewed-on: https://go-review.googlesource.com/12438Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/compile/internal/gc/testdata/short_ssa.go

-// compile
+// run
 
 // Copyright 2015 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style