keys: fix trusted/encrypted keys sparse rcu_assign_pointer messages

Define rcu_assign_keypointer(), which uses the key payload.rcudata instead
of payload.data, to resolve the CONFIG_SPARSE_RCU_POINTER message:
"incompatible types in comparison expression (different address spaces)"

Replace the rcu_assign_pointer() calls in encrypted/trusted keys with
rcu_assign_keypointer().

Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>
diff --git a/security/keys/encrypted-keys/encrypted.c b/security/keys/encrypted-keys/encrypted.c
index 41144f7..d91efb6 100644
--- a/security/keys/encrypted-keys/encrypted.c
+++ b/security/keys/encrypted-keys/encrypted.c
@@ -810,7 +810,7 @@
 		goto out;
 	}
 
-	rcu_assign_pointer(key->payload.data, epayload);
+	rcu_assign_keypointer(key, epayload);
 out:
 	kfree(datablob);
 	return ret;
@@ -874,7 +874,7 @@
 	memcpy(new_epayload->payload_data, epayload->payload_data,
 	       epayload->payload_datalen);
 
-	rcu_assign_pointer(key->payload.data, new_epayload);
+	rcu_assign_keypointer(key, new_epayload);
 	call_rcu(&epayload->rcu, encrypted_rcu_free);
 out:
 	kfree(buf);