drm/xe: xe_hw_engine_class: Add fault injection and improve error handling in kobj_xe_hw_engine_class

[Sobin Thomas <sobin.thomas@intel.com>]

- Added fault injection for `kobj_xe_hw_engine_class` to enhance coverage.
- Improved error handling by checking for `IS_ERR_OR_NULL` on `keclass` and
  propagating the error using `PTR_ERR`.

Can be tested using inject-fault-probe-function-kobj_xe_hw_engine_class

Signed-off-by: Sobin Thomas <sobin.thomas@intel.com>
---
 drivers/gpu/drm/xe/xe_hw_engine_class_sysfs.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/xe/xe_hw_engine_class_sysfs.c b/drivers/gpu/drm/xe/xe_hw_engine_class_sysfs.c
index 640950172088..0cafe1175389 100644
--- a/drivers/gpu/drm/xe/xe_hw_engine_class_sysfs.c
+++ b/drivers/gpu/drm/xe/xe_hw_engine_class_sysfs.c
@@ -571,6 +571,7 @@ kobj_xe_hw_engine_class(struct xe_device *xe, struct kobject *parent, const char
 
 	return keclass;
 }
+ALLOW_ERROR_INJECTION(kobj_xe_hw_engine_class, NULL);
 
 static void hw_engine_class_defaults_fini(void *arg)
 {
@@ -662,8 +663,8 @@ int xe_hw_engine_class_sysfs_init(struct xe_gt *gt)
 		}
 
 		keclass = kobj_xe_hw_engine_class(xe, kobj, name);
-		if (!keclass) {
-			err = -EINVAL;
+		if (IS_ERR_OR_NULL(keclass)) {
+			err = PTR_ERR(keclass);
 			goto err_object;
 		}
 
-- 
2.34.1