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: dd08ebf6c3 ("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>

drivers/gpu/drm/xe/xe_guc_pc.c

@@ -1073,7 +1073,7 @@ int xe_guc_pc_start(struct xe_guc_pc *pc)
 		goto out;
 	}
 
-	memset(pc->bo->vmap.vaddr, 0, size);
+	xe_map_memset(xe, &pc->bo->vmap, 0, 0, size);
 	slpc_shared_data_write(pc, header.size, size);
 
 	earlier = ktime_get();