drm/nv04-nv40: Fix up the programmed horizontal sync pulse delay.

The calculated values were a little bit off (~16 clocks), the only
effect it could have had is a slightly offset image with respect to
the blob on analog outputs (bug 26790).

Signed-off-by: Francisco Jerez <currojerez@riseup.net>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>