drm/xe: Restore EIO errno return when GuC PC start fails

Commit b4b05e5 ("drm/xe/guc_pc: Retry and wait longer for GuC PC
start"), leads to the following Smatch static checker warning:

        drivers/gpu/drm/xe/xe_guc_pc.c:1073 xe_guc_pc_start()
        warn: missing error code here? '_dev_err()' failed. 'ret' = '0'

Fixes: c605acb ("drm/xe/guc_pc: Retry and wait longer for GuC PC start")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/intel-xe/1454a5f1-ee18-4df1-a6b2-a4a3dddcd1cb@stanley.mountain/
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://lore.kernel.org/r/20250328181752.26677-1-rodrigo.vivi@intel.com
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
(cherry picked from commit 3f2bdcc)
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>

Author: rodrigovivi

drivers/gpu/drm/xe/xe_guc_pc.c

@@ -1070,6 +1070,7 @@ int xe_guc_pc_start(struct xe_guc_pc *pc)
 		if (wait_for_pc_state(pc, SLPC_GLOBAL_STATE_RUNNING,
 				      SLPC_RESET_EXTENDED_TIMEOUT_MS)) {
 			xe_gt_err(gt, "GuC PC Start failed: Dynamic GT frequency control and GT sleep states are now disabled.\n");
+			ret = -EIO;
 			goto out;
 		}