crypto: mxs-dcp: Check the return value of stmp_reset_block()

stmp_reset_block() may fail, so check its return value and propagate it in the
case of error.

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>