drm/msm: Avoid rounding up to one jiffy

If userspace is trying to achieve a timeout of zero, let 'em have it.
Only round up if the timeout is greater than zero.

Fixes: 4969bccd ("drm/msm: Avoid rounding down to zero jiffies")
Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Akhil P Oommen <quic_akhilpo@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/632264/