crypto: caam - fix typo in dma_mapping_error

dma_mapping_error checks for an incorrect DMA address:
s/ctx->sh_desc_enc_dma/ctx->sh_desc_dec_dma

Signed-off-by: Horia Geanta <horia.geanta@freescale.com>
Acked-by: Kim Phillips <kim.phillips@freescale.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>