runtime: use raceprocctx in race_arm64

In CL 169960 I didn't realize that we also have race detector support for arm64.

Change-Id: If77bfb0f700a04c04416dad61ef11e27b1c98e07
Reviewed-on: https://go-review.googlesource.com/c/go/+/170105
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

src/runtime/race_arm64.s

@@ -427,7 +427,7 @@ TEXT	runtime·racecallbackthunk(SB), NOSPLIT|NOFRAME, $0
 	load_g
 	MOVD	g_m(g), R0
 	MOVD	m_p(R0), R0
-	MOVD	p_racectx(R0), R0
+	MOVD	p_raceprocctx(R0), R0
 	MOVD	R0, (R1)
 	MOVD	R13, g
 	JMP	(LR)