crypto: atmel-i2c - add missing arg description

Add missing description for argument hwrng.
Signed-off-by: Lothar Rubusch <l.rubusch@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/crypto/atmel-i2c.h

@@ -124,6 +124,7 @@ struct atmel_ecc_driver_data {
  * @wake_token          : wake token array of zeros
  * @wake_token_sz       : size in bytes of the wake_token
  * @tfm_count           : number of active crypto transformations on i2c client
+ * @hwrng               : hold the hardware generated rng
  *
  * Reads and writes from/to the i2c client are sequential. The first byte
  * transmitted to the device is treated as the byte size. Any attempt to send