drm/xe: Convert memory device refcount to s32

The comparison with < 0 suggests that the memory device access
should be signed to handle underflow. This makes it work more reliably.

As a result, the max refcount is now S32_MAX instead.
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

drivers/gpu/drm/xe/xe_device.c

@@ -351,7 +351,7 @@ void xe_device_mem_access_get(struct xe_device *xe)
 	if (resumed)
 		xe_pm_runtime_put(xe);
 
-	XE_WARN_ON(xe->mem_access.ref == U32_MAX);
+	XE_WARN_ON(xe->mem_access.ref == S32_MAX);
 }
 
 void xe_device_mem_access_put(struct xe_device *xe)

drivers/gpu/drm/xe/xe_device_types.h

@@ -173,7 +173,7 @@ struct xe_device {
 		/** @lock: protect the ref count */
 		struct mutex lock;
 		/** @ref: ref count of memory accesses */
-		u32 ref;
+		s32 ref;
 		/** @hold_rpm: need to put rpm ref back at the end */
 		bool hold_rpm;
 	} mem_access;