crypto: caam - fix DMA mapping xcbc key twice

Fix a side effect of adding xcbc support, which leads to DMA mapping the
key twice.

Fixes: 12b8567f ("crypto: caam - add support for xcbc(aes)")
Signed-off-by: Horia Geantă <horia.geanta@nxp.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>