x86: Use the correct SPDX License Identifier in headers

Correct the SPDX License Identifier format in a couple of headers.
Suggested-by: Joe Perches <joe@perches.com>
Signed-off-by: Nishad Kamdar <nishadkamdar@gmail.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Cc: Waiman Long <longman@redhat.com>
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/697848ff866ade29e78e872525d7a3067642fd37.1555427420.git.nishadkamdar@gmail.com

arch/x86/include/asm/cpu_entry_area.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 
 #ifndef _ASM_X86_CPU_ENTRY_AREA_H
 #define _ASM_X86_CPU_ENTRY_AREA_H

arch/x86/include/asm/pti.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 #ifndef _ASM_X86_PTI_H
 #define _ASM_X86_PTI_H
 #ifndef __ASSEMBLY__

arch/x86/kernel/process.h

-// SPDX-License-Identifier: GPL-2.0
+/* SPDX-License-Identifier: GPL-2.0 */
 //
 // Code shared between 32 and 64 bit