intel_th: msu: Fix an uninitialized mutex

Commit 615c164d ("intel_th: msu: Introduce buffer interface") added a
mutex that it forgot to initialize, resulting in a lockdep splat.

Fix that by initializing the mutex statically.
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Fixes: 615c164d ("intel_th: msu: Introduce buffer interface")
Link: https://lore.kernel.org/r/20191028070651.9770-3-alexander.shishkin@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hwtracing/intel_th/msu.c

@@ -164,7 +164,7 @@ struct msc {
 };
 
 static LIST_HEAD(msu_buffer_list);
-static struct mutex msu_buffer_mutex;
+static DEFINE_MUTEX(msu_buffer_mutex);
 
 /**
  * struct msu_buffer_entry - internal MSU buffer bookkeeping