drm/i915: Correct the variable holding the value for EOT to write

This isuue got introduced in -

commit 24ee0e64
Author: Gaurav K Singh <gaurav.k.singh@intel.com>
Date:   Fri Dec 5 14:24:21 2014 +0530

    drm/i915: Update the DSI enable path to support dual

Signed-off-by: Shobhit Kumar <shobhit.kumar@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>