crypto: amcc - Do a NULL check for pointer

Compare pointer-typed values to NULL rather than 0.

The semantic patch that makes this change is available
in scripts/coccinelle/null/badzero.cocci

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>