cpu: use t.Fatal instead of t.Fatalf

The messages contain no format string, so there is no need to use
t.Fatalf.

Change-Id: I29098c04797f919784b732af84a63fbaed671558
Reviewed-on: https://go-review.googlesource.com/111776
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

cpu/cpu_test.go

@@ -14,7 +14,7 @@ import (
 func TestAMD64minimalFeatures(t *testing.T) {
 	if runtime.GOARCH == "amd64" {
 		if !cpu.X86.HasSSE2 {
-			t.Fatalf("HasSSE2 expected true, got false")
+			t.Fatal("HasSSE2 expected true, got false")
 		}
 	}
 }
@@ -22,7 +22,7 @@ func TestAMD64minimalFeatures(t *testing.T) {
 func TestAVX2hasAVX(t *testing.T) {
 	if runtime.GOARCH == "amd64" {
 		if cpu.X86.HasAVX2 && !cpu.X86.HasAVX {
-			t.Fatalf("HasAVX expected true, got false")
+			t.Fatal("HasAVX expected true, got false")
 		}
 	}
 }