crypto: mxs-dcp: Use devm_kzalloc()

Using devm_kzalloc() can make the code cleaner.

While at it, remove the devm_kzalloc error message as there is standard OOM
message done by the core.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Marek Vasut <marex@denx.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>