runtime: fix restoring PC in ARM version of cgocallback_gofunc

Fixes #15856.

Change-Id: Ia8def161642087e4bd92a87298c77a0f9f83dc86
Reviewed-on: https://go-review.googlesource.com/23586
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Elias Naur <elias.naur@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

src/runtime/asm_arm.s

@@ -626,7 +626,7 @@ havem:
 	BL	runtime·cgocallbackg(SB)
 
 	// Restore g->sched (== m->curg->sched) from saved values.
-	MOVW	4(R13), R5
+	MOVW	0(R13), R5
 	MOVW	R5, (g_sched+gobuf_pc)(g)
 	MOVW	$12(R13), R4
 	MOVW	R4, (g_sched+gobuf_sp)(g)