drm/i915: Use round to closest when computing the CEA 1.001 pixel clocks

drm_edid.c now computes the alternate CEA clocks using
DIV_ROUND_CLOSEST(), so follow suit in the N/CTS setup to make sure we
pick the right setting for the mode.

Unfortunately we can't actually use DIV_ROUND_CLOSEST() here due to the
({}) construct used, so just stick in raw numbers instead.

Cc: Clint Taylor <clinton.a.taylor@intel.com>
Cc: Libin Yang <libin.yang@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>