crypto: aead - move aead_request_cast helper to aead.h

Move the helper function to common header for everybody to use.

changes in v2:
- move the helper to crypto/internal/aead.h
  instead of crypto/aead.h

Signed-off-by: Tadeusz Struk <tadeusz.struk@intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/crypto/atmel-aes.c

@@ -369,12 +369,6 @@ static inline size_t atmel_aes_padlen(size_t len, size_t block_size)
 	return len ? block_size - len : 0;
 }
 
-static inline struct aead_request *
-aead_request_cast(struct crypto_async_request *req)
-{
-	return container_of(req, struct aead_request, base);
-}
-
 static struct atmel_aes_dev *atmel_aes_find_dev(struct atmel_aes_base_ctx *ctx)
 {
 	struct atmel_aes_dev *aes_dd = NULL;