usr.sbin/bhyve: send an initialized value to wake up blocking kqueue

This is a no-op initialization because nothing reads this value.  "This
wasn't wrong previously, but this is more correct now." -imp

Coverity CID:	1194307
Approved by:	markj, imp, scottl
Differential Revision:	https://reviews.freebsd.org/D20921

usr.sbin/bhyve/mevent.c

@@ -119,7 +119,7 @@ mevent_pipe_read(int fd, enum ev_type type, void *param)
 static void
 mevent_notify(void)
 {
-	char c;
+	char c = '\0';
 	
 	/*
 	 * If calling from outside the i/o thread, write a byte on the