drm/xe: Fix missing runtime PM reference in ccs_mode_store

drm/xe: Fix missing runtime PM reference in ccs_mode_store

ccs_mode_store() calls xe_gt_reset() which internally invokes
xe_pm_runtime_get_noresume(). That function requires the caller
to already hold an outer runtime PM reference and warns if none
is held:

  [46.891177] xe 0000:03:00.0: [drm] Missing outer runtime PM protection
  [46.891178] WARNING: drivers/gpu/drm/xe/xe_pm.c:885 at
  xe_pm_runtime_get_noresume+0x8b/0xc0

Fix this by protecting xe_gt_reset() with the scope-based
guard(xe_pm_runtime)(xe), which is the preferred form when
the reference lifetime matches a single scope.

v2:
- Use scope-based guard(xe_pm_runtime)(xe) (Shuicheng)
- Update commit message accordingly

Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/7593
Fixes: 480b358e7d8e ("drm/xe: Do not wake device during a GT reset")
Cc: <stable@vger.kernel.org> # v6.19+
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Shuicheng Lin <shuicheng.lin@intel.com>
Suggested-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Sanjay Yadav <sanjay.kumar.yadav@intel.com>
Reviewed-by: Shuicheng Lin <shuicheng.lin@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patch.msgid.link/20260313071608.3459480-2-sanjay.kumar.yadav@intel.com
(cherry picked from commit 7937ea733f79b3f25e802a0c8360bf7423856f36)
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>