crypto: sa2ul - Fix memory leak of rxd

There are two error return paths that are not freeing rxd and causing
memory leaks.  Fix these.

Addresses-Coverity: ("Resource leak")
Fixes: 00c9211f

 ("crypto: sa2ul - Fix DMA mapping API usage")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>