nds32: Fix empty call trace

The compiler predefined macro 'NDS32_ABI_2' had been removed, it should
use the '__NDS32_ABI_2' here.

Signed-off-by: Zong Li <zong@andestech.com>
Acked-by: Greentime Hu <greentime@andestech.com>
Signed-off-by: Greentime Hu <greentime@andestech.com>