[HIFN]: Fix max queue length value

All but the last element of the command and result descriptor rings can be
used for crypto requests, fix HIFN_QUEUE_LENGTH.
    
Signed-off-by: Patrick McHardy <kaber@trash.net>
Acked-by: Evgeniy Polyakov <johnpol@2ka.mipt.ru>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/crypto/hifn_795x.c

@@ -371,7 +371,7 @@ static atomic_t hifn_dev_number;
 
 #define HIFN_D_DST_DALIGN		4
 
-#define HIFN_QUEUE_LENGTH		HIFN_D_CMD_RSIZE-5
+#define HIFN_QUEUE_LENGTH		HIFN_D_CMD_RSIZE-1
 
 #define AES_MIN_KEY_SIZE		16
 #define AES_MAX_KEY_SIZE		32