drm/i915: fix i9xx_crtc_clock_get for multiplied pixels

The dpll actually runs at the port clock so we don't need
to multiply it again with the pixel multiplier to get the
adjusted_mode.clock. This is in contrast to the ironlake
pixel clock readout code which uses the fdi dotclock: That
one does _not_ run with multiplied pixels.

This issue goes back to the original clock readout code added
in

commit f1f644dc
Author: Jesse Barnes <jbarnes@virtuousgeek.org>
Date:   Thu Jun 27 00:39:25 2013 +0300

    drm/i915: get mode clock when reading the pipe config v9

Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>