drm/amdkfd: fix resource_size.cocci warnings

Use resource_size function on resource object
instead of explicit computation.

Clean up coccicheck warning:
./drivers/gpu/drm/amd/amdkfd/kfd_migrate.c:905:10-13: ERROR: Missing
resource_size with res

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Reviewed-by: Amos Kong <kongjianjun@gmail.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdkfd/kfd_migrate.c

@@ -901,8 +901,7 @@ int svm_migrate_init(struct amdgpu_device *adev)
 
 		/* Disable SVM support capability */
 		pgmap->type = 0;
-		devm_release_mem_region(adev->dev, res->start,
-					res->end - res->start + 1);
+		devm_release_mem_region(adev->dev, res->start, resource_size(res));
 		return PTR_ERR(r);
 	}