drm/i915/guc: fix NULL vs IS_ERR() checking

The intel_engine_create_virtual() function does not return NULL.  It
returns error pointers.

Fixes: e5e32171 ("drm/i915/guc: Connect UAPI to GuC multi-lrc interface")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211116114916.GB11936@kili

drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c

@@ -3079,8 +3079,8 @@ guc_create_parallel(struct intel_engine_cs **engines,
 
 		ce = intel_engine_create_virtual(siblings, num_siblings,
 						 FORCE_VIRTUAL);
-		if (!ce) {
-			err = ERR_PTR(-ENOMEM);
+		if (IS_ERR(ce)) {
+			err = ERR_CAST(ce);
 			goto unwind;
 		}