cmd/godoc: fix tests for cmd/compile refactorings

In golang.org/cl/38089, I removed all of the prog.go files.

Change-Id: I4d8dd021a62b5d6d8b7cb5cfe0ecd7268812805c
Reviewed-on: https://go-review.googlesource.com/38432
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

cmd/godoc/godoc_test.go

@@ -275,7 +275,7 @@ func testWeb(t *testing.T, withIndex bool) {
 		{
 			path: "/cmd/compile/internal/amd64/",
 			match: []string{
-				`href="/src/cmd/compile/internal/amd64/prog.go"`,
+				`href="/src/cmd/compile/internal/amd64/ssa.go"`,
 			},
 		},
 	}