crypto: atmel-ecc - Struct headers need to start with keyword 'struct'

Fixes the following W=1 kernel build warning(s):

drivers/crypto/atmel-ecc.c:41: warning: cannot understand function prototype: 'struct atmel_ecdh_ctx '

Cc: Tudor Ambarus <[e-mail]>
Cc: Herbert Xu <[e-mail]>
Cc: "David S. Miller" <[e-mail]>
Cc: Nicolas Ferre <[e-mail]>
Cc: Alexandre Belloni <[e-mail]>
Cc: Ludovic Desroches <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Signed-off-by: Lee Jones <[e-mail]>
Reviewed-by: Tudor Ambarus <[e-mail]>
Signed-off-by: Herbert Xu <[e-mail]>

drivers/crypto/atmel-ecc.c

···
 static struct atmel_ecc_driver_data driver_data;
 
 /**
- * atmel_ecdh_ctx - transformation context
+ * struct atmel_ecdh_ctx - transformation context
  * @client     : pointer to i2c client device
  * @fallback   : used for unsupported curves or when user wants to use its own
  *               private key.