crypto: hisilicon/debugfs - Fix debugfs uninit process issue

During the zip probe process, the debugfs failure does not stop
the probe. When debugfs initialization fails, jumping to the
error branch will also release regs, in addition to its own
rollback operation.

As a result, it may be released repeatedly during the regs
uninit process. Therefore, the null check needs to be added to
the regs uninit process.

Signed-off-by: Chenghai Huang <huangchenghai2@huawei.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>