drm/i915: Bump HDMI min port clock to 25 MHz

drm/i915: Bump HDMI min port clock to 25 MHz

Increase the HDMI port minimum port clock from 20 to 25 MHz. This is
is the minimum listed in the DVI/HDMI specs, and it's also the
documented minimum DPLL frequency for most of our platforms.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-and-tested-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>