drm/xe: Fix memset on iomem

drm/xe: Fix memset on iomem

It should rather use xe_map_memset() as the BO is created with
XE_BO_FLAG_VRAM_IF_DGFX in xe_guc_pc_init().

Fixes: dd08ebf6c352 ("drm/xe: Introduce a new DRM driver for Intel GPUs")
Cc: stable@vger.kernel.org
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://lore.kernel.org/r/20250612-vmap-vaddr-v1-1-26238ed443eb@intel.com
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
(cherry picked from commit 21cf47d89fba353b2d5915ba4718040c4cb955d3)
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>