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>
diff --git a/drivers/hv/hv_trace.h b/drivers/hv/hv_trace.h
index d635ee9..999f80a 100644
--- a/drivers/hv/hv_trace.h
+++ b/drivers/hv/hv_trace.h
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0
+
 #undef TRACE_SYSTEM
 #define TRACE_SYSTEM hyperv