crypto: caam - fix hash context DMA unmap size

When driver started using state->caam_ctxt for storing both running hash
and final hash, it was not updated to handle different DMA unmap
lengths.

Cc: <stable@vger.kernel.org> # v4.19+
Fixes: c19650d6 ("crypto: caam - fix DMA mapping of stack memory")
Signed-off-by: Franck LENORMAND <franck.lenormand@nxp.com>
Signed-off-by: Horia Geantă <horia.geanta@nxp.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>