drm/i915: Fix TV Out refresh rate.

TV Out refresh rate was half of the specification for almost all modes.
Due to this reason pixel clock was so low for some modes causing flickering screen.

Signed-off-by: Rodrigo Vivi <rodrigo.vivi@gmail.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Keith Packard <keithp@keithp.com>