Fix incorrect EXPORT_SYMBOL().

Fixes: efca1398 ("RISC-V: Introduce a new config for SBI v0.1")
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>