drm/xe: Use __iomem for the regs pointer

The regs pointer points to IO memory. Annotate it properly and
fix the corresponding sparse warning.

Fixes: a4e2f3a ("drm/xe: refactor xe_mmio_probe_tiles to support MMIO extension")
Cc: Koby Elbaz <kelbaz@habana.ai>
Cc: Ofir Bitton <obitton@habana.ai>
Cc: Moti Haimovski <mhaimovski@habana.ai>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240109112405.108136-2-thomas.hellstrom@linux.intel.com
(cherry picked from commit 9d03bf3)
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>

Author: Thomas Hellström

drivers/gpu/drm/xe/xe_mmio.c

@@ -303,7 +303,7 @@ void xe_mmio_probe_tiles(struct xe_device *xe)
 	u8 id, tile_count = xe->info.tile_count;
 	struct xe_gt *gt = xe_root_mmio_gt(xe);
 	struct xe_tile *tile;
-	void *regs;
+	void __iomem *regs;
 	u32 mtcfg;
 
 	if (tile_count == 1)