drm/nouveau/ltc/gf100: use more reasonable timeout value

LTC operations timeout was set to 2ms, which may be too low for devices
that run at very low clocks (e.g. GM20B) and trigger timeout messages.

Set the timeout to the default 2s. Also remove the redundant error
messages since nvkm_wait_msec() will already display a warning.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>