freedreno/drm: Don't miscalculate timeout

The current code overflows (s * 1000000000) for s >= 5 but that is e.g. used in msm_bo_cpu_prep.

I have no actual hardware to test but it's the same code as in !3509 (merged)

Signed-off-by: Guido Günther agx@sigxcpu.org