crypto: aead - fix kernel-doc warnings in crypto/aead.h

Fix 21 occurrences of this kernel-doc warning in <crypto/aead.h>:

..//include/crypto/aead.h:149: warning: No description found for parameter 'base'
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

include/crypto/aead.h

@@ -128,6 +128,7 @@ struct aead_request {
  * @exit: Deinitialize the cryptographic transformation object. This is a
  *	  counterpart to @init, used to remove various changes set in
  *	  @init.
+ * @base: Definition of a generic crypto cipher algorithm.
  *
  * All fields except @ivsize is mandatory and must be filled.
  */