crypto: qat - fix potential spectre issue

Sanitize ring_num value coming from configuration (and potentially
from user space) before it is used as index in the banks array.

This issue was detected by smatch:

    drivers/crypto/qat/qat_common/adf_transport.c:233 adf_create_ring() warn: potential spectre issue 'bank->rings' [r] (local cap)
Signed-off-by: Adam Guerin <adam.guerin@intel.com>
Reviewed-by: Giovanni Cabiddu <giovanni.cabiddu@intel.com>
Signed-off-by: Giovanni Cabiddu <giovanni.cabiddu@intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/crypto/qat/qat_common/adf_transport.c

 // SPDX-License-Identifier: (BSD-3-Clause OR GPL-2.0-only)
 /* Copyright(c) 2014 - 2020 Intel Corporation */
 #include <linux/delay.h>
+#include <linux/nospec.h>
 #include "adf_accel_devices.h"
 #include "adf_transport_internal.h"
 #include "adf_transport_access_macros.h"
@@ -246,6 +247,7 @@ int adf_create_ring(struct adf_accel_dev *accel_dev, const char *section,
 		return -EFAULT;
 	}
 
+	ring_num = array_index_nospec(ring_num, num_rings_per_bank);
 	bank = &transport_data->banks[bank_num];
 	if (adf_reserve_ring(bank, ring_num)) {
 		dev_err(&GET_DEV(accel_dev), "Ring %d, %s already exists.\n",