runtime/race: fix test so it compiles

I'm not sure what the convert function was intended to be.

Fixes #14011

Change-Id: I29d905bc1827936b9433b20b13b7a0b0ac5f502e
Reviewed-on: https://go-review.googlesource.com/18712Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/runtime/race/testdata/issue12225_test.go

@@ -4,9 +4,16 @@
 
 package race_test
 
+import "unsafe"
+
 // golang.org/issue/12225
 // The test is that this compiles at all.
 
+//go:noinline
+func convert(s string) []byte {
+	return []byte(s)
+}
+
 func issue12225() {
 	println(*(*int)(unsafe.Pointer(&convert("")[0])))
 	println(*(*int)(unsafe.Pointer(&[]byte("")[0])))