drm/xe: Annotate xe_ttm_stolen_mgr::mapping with __iomem

The pointer points to IO memory, but the __iomem annotation was
incorrectly placed. Annotate it correctly, update its usage accordingly
and fix the corresponding sparse error.

Fixes: d8b52a0 ("drm/xe: Implement stolen memory.")
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
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/20240109112405.108136-5-thomas.hellstrom@linux.intel.com
(cherry picked from commit dcddb6f)
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>

Author: Thomas Hellström

drivers/gpu/drm/xe/xe_ttm_stolen_mgr.c

@@ -31,7 +31,7 @@ struct xe_ttm_stolen_mgr {
 	/* GPU base offset */
 	resource_size_t stolen_base;
 
-	void *__iomem mapping;
+	void __iomem *mapping;
 };
 
 static inline struct xe_ttm_stolen_mgr *
@@ -275,7 +275,7 @@ static int __xe_ttm_stolen_io_mem_reserve_bar2(struct xe_device *xe,
 	drm_WARN_ON(&xe->drm, !(mem->placement & TTM_PL_FLAG_CONTIGUOUS));
 
 	if (mem->placement & TTM_PL_FLAG_CONTIGUOUS && mgr->mapping)
-		mem->bus.addr = (u8 *)mgr->mapping + mem->bus.offset;
+		mem->bus.addr = (u8 __force *)mgr->mapping + mem->bus.offset;
 
 	mem->bus.offset += mgr->io_base;
 	mem->bus.is_iomem = true;