hv: add SPDX license to trace

Missing license on Hyper-V VMBUS tracing files.

Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hv/hv_trace.c

@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0
+
 #include "hyperv_vmbus.h"
 
 #define CREATE_TRACE_POINTS