crypto: bcm - add error check in the ahash_hmac_init function

The ahash_init functions may return fails. The ahash_hmac_init should
not return ok when ahash_init returns error. For an example, ahash_init
will return -ENOMEM when allocation memory is error.

Fixes: 9d12ba86 ("crypto: brcm - Add Broadcom SPU driver")
Signed-off-by: Chen Ridong <chenridong@huawei.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>