tools: hv: Use the correct style for SPDX License Identifier

This patch corrects the SPDX License Identifier style
in the trace header file related to Microsoft Hyper-V
client drivers.
For C header files Documentation/process/license-rules.rst
mandates C-like comments (opposed to C source files where
C++ style should be used)

Changes made by using a script provided by Joe Perches here:
https://lkml.org/lkml/2019/2/7/46Suggested-by: NJoe Perches <joe@perches.com>
Signed-off-by: NNishad Kamdar <nishadkamdar@gmail.com>
Acked-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NSasha Levin <sashal@kernel.org>

drivers/hv/hv_trace.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 
 #undef TRACE_SYSTEM
 #define TRACE_SYSTEM hyperv