drm/nouveau/ibus/gf100: increase wait timeout to avoid read faults

Increase clock timeout of some unknown engines in order to avoid failure
at high gpcclk rate.

This fixes IBUS read faults on my GF119 when reclocking is manually
enabled. Note that memory reclocking is completely broken and NvMemExec
has to be disabled to allow core clock reclocking only.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>