Remove readability refactor for failover auth to fix clang warning (#1481)

As part of #1463, I made a small refactor between the PR and the daily
test I submitted to try to improve readability by adding a function to
abstract the extraction of the message types. However, that change
apparently caused GCC to throw another warning, so reverting the
abstraction on just one line.

Signed-off-by: Madelyn Olson <[email protected]>
Signed-off-by: Jacob Murphy <[email protected]>

Author: madolson

src/cluster_legacy.c

@@ -4289,7 +4289,7 @@ void clusterRequestFailoverAuth(void) {
     /* If this is a manual failover, set the CLUSTERMSG_FLAG0_FORCEACK bit
      * in the header to communicate the nodes receiving the message that
      * they should authorized the failover even if the primary is working. */
-    if (server.cluster->mf_end) getMessageFromSendBlock(msgblock)->mflags[0] |= CLUSTERMSG_FLAG0_FORCEACK;
+    if (server.cluster->mf_end) msgblock->data[0].msg.mflags[0] |= CLUSTERMSG_FLAG0_FORCEACK;
     clusterBroadcastMessage(msgblock);
     clusterMsgSendBlockDecrRefCount(msgblock);
 }