drm/amdgpu: fix SPDX header on amd_cper.h

This should be MIT.  The driver in general is MIT and
the license text at the top of the file is MIT so fix
it.

Fixes: 523b69c654 ("drm/amd/include: Add amd cper header")
Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/4654
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 72c5482cb0)

drivers/gpu/drm/amd/include/amd_cper.h

@@ -1,4 +1,4 @@
-/* SPDX-License-Identifier: GPL-2.0 */
+/* SPDX-License-Identifier: MIT */
 /*
  * Copyright 2025 Advanced Micro Devices, Inc.
  *