drm/msm/dpu: fix incorrect type for ret

Change 'ret' from unsigned long to int, as storing negative error codes
in an unsigned long makes it never equal to -ETIMEDOUT, causing logical
errors.

Fixes: d7d0e73 ("drm/msm/dpu: introduce the dpu_encoder_phys_* for writeback")
Signed-off-by: Qianfeng Rong <rongqianfeng@vivo.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Patchwork: https://patchwork.freedesktop.org/patch/671100/
Link: https://lore.kernel.org/r/20250826092047.224341-1-rongqianfeng@vivo.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>

Author: qianfengrong

drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_wb.c

@@ -446,7 +446,7 @@ static void _dpu_encoder_phys_wb_handle_wbdone_timeout(
 static int dpu_encoder_phys_wb_wait_for_commit_done(
 		struct dpu_encoder_phys *phys_enc)
 {
-	unsigned long ret;
+	int ret;
 	struct dpu_encoder_wait_info wait_info;
 	struct dpu_encoder_phys_wb *wb_enc = to_dpu_encoder_phys_wb(phys_enc);