crypto: inside-secure - avoid unmapping DMA memory that was not mapped

This patch adds a parameter in the SafeXcel ahash request structure to
keep track of the number of SG entries mapped. This allows not to call
dma_unmap_sg() when dma_map_sg() wasn't called in the first place. This
also removes a warning when the debugging of the DMA-API is enabled in
the kernel configuration: "DMA-API: device driver tries to free DMA
memory it has not allocated".

Cc: stable@vger.kernel.org
Fixes: 1b44c5a6 ("crypto: inside-secure - add SafeXcel EIP197 crypto engine driver")
Signed-off-by: Antoine Tenart <antoine.tenart@free-electrons.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>