drm/radeon: fix incorrrect SPDX-License-Identifiers

drm/radeon: fix incorrrect SPDX-License-Identifiers

radeon is MIT.  This were incorrectly changed in
commit b24413180f56 ("License cleanup: add SPDX GPL-2.0 license identifier to files with no license")
and
commit d198b34f3855 (".gitignore: add SPDX License Identifier")
and:
commit ec8f24b7faaf ("treewide: Add SPDX license identifier - Makefile/Kconfig")

Fixes: d198b34f3855 (".gitignore: add SPDX License Identifier")
Fixes: ec8f24b7faaf ("treewide: Add SPDX license identifier - Makefile/Kconfig")
Fixes: b24413180f56 ("License cleanup: add SPDX GPL-2.0 license identifier to files with no license")
Bug: https://gitlab.freedesktop.org/drm/amd/-/issues/2053
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>