crypto: amlogic - ensure error variable err is set before returning it

Currently when the call to crypto_engine_alloc_init fails the error
return path returns an uninitialized value in the variable err. Fix
this by setting err to -ENOMEM.

Addresses-Coverity: ("Uninitialized scalar variable")
Fixes: 48fe583f

 ("crypto: amlogic - Add crypto accelerator for amlogic GXL")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Corentin Labbe <clabbe@baylibre.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>