drm/i915: Multiply the refresh by 1000 in TV mode validatiion

As of 559ee21d

 the actual refresh rate
is returned by the function of drm_mode_vrefresh, so multiply the refresh
rate by 1000 in TV mode validation.

At the same time the error is expanded from 10 to 1000.

Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
Signed-off-by: Eric Anholt <eric@anholt.net>