switch keyctl_instantiate_key_common() to iov_iter

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/security/keys/internal.h b/security/keys/internal.h
index 200e378..5105c2c 100644
--- a/security/keys/internal.h
+++ b/security/keys/internal.h
@@ -243,9 +243,10 @@
 				       unsigned, key_serial_t);
 extern long keyctl_invalidate_key(key_serial_t);
 
+struct iov_iter;
 extern long keyctl_instantiate_key_common(key_serial_t,
-					  const struct iovec *,
-					  unsigned, size_t, key_serial_t);
+					  struct iov_iter *,
+					  key_serial_t);
 #ifdef CONFIG_PERSISTENT_KEYRINGS
 extern long keyctl_get_persistent(uid_t, key_serial_t);
 extern unsigned persistent_keyring_expiry;