crypto: img-hash - Fix null pointer exception

Sporadic null pointer exceptions came from here. Fix them.

Signed-off-by: Will Thomas <will.thomas@imgtec.com>
Reviewed-by: James Hartley <james.hartley@imgtec.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
diff --git a/drivers/crypto/img-hash.c b/drivers/crypto/img-hash.c
index 68e8aa9..e5c941b 100644
--- a/drivers/crypto/img-hash.c
+++ b/drivers/crypto/img-hash.c
@@ -361,7 +361,7 @@
 	size_t nbytes, bleft, wsend, len, tbc;
 	struct scatterlist tsg;
 
-	if (!ctx->sg)
+	if (!hdev->req || !ctx->sg)
 		return;
 
 	addr = sg_virt(ctx->sg);