crypto: cavium/nitrox - dma_mapping_error() returns bool

We want to return negative error codes here, but we're accidentally
propogating the "true" return from dma_mapping_error().

Fixes: 14fa93cd ("crypto: cavium - Add support for CNN55XX adapters.")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>