crypto: engine - delete duplicated word

Drop the doubled word "a".

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: linux-crypto@vger.kernel.org
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/crypto_engine.c

@@ -466,7 +466,7 @@ EXPORT_SYMBOL_GPL(crypto_engine_stop);
  * crypto-engine queue.
  * @dev: the device attached with one hardware engine
  * @retry_support: whether hardware has support for retry mechanism
- * @cbk_do_batch: pointer to a callback function to be invoked when executing a
+ * @cbk_do_batch: pointer to a callback function to be invoked when executing
  *                a batch of requests.
  *                This has the form:
  *                callback(struct crypto_engine *engine)