libcamera: Correct include headers for Mutex classes

Mutex classes are defined in mutex.h. This replaces thread.h
include for the Mutex classes with mutex.h.

Signed-off-by: Hirokazu Honda <hiroh@chromium.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Umang Jain <umang.jain@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/libcamera/base/thread.cpp

@@ -17,6 +17,7 @@
 #include <libcamera/base/event_dispatcher_poll.h>
 #include <libcamera/base/log.h>
 #include <libcamera/base/message.h>
+#include <libcamera/base/mutex.h>
 
 /**
  * \page thread Thread Support