accel/tcg: Replace CPUState.env_ptr with cpu_env()

Reviewed-by: Anton Johansson <anjo@rev.ng>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

linux-user/i386/cpu_loop.c

@@ -323,7 +323,7 @@ void cpu_loop(CPUX86State *env)
 
 static void target_cpu_free(void *obj)
 {
-    CPUArchState *env = ((CPUState *)obj)->env_ptr;
+    CPUArchState *env = cpu_env(obj);
     target_munmap(env->gdt.base, sizeof(uint64_t) * TARGET_GDT_ENTRIES);
     g_free(obj);
 }