drm: fix lut value extraction function

When extracting the value at full precision (16 bits), no need to
round the value.

This was spotted by Jani when running sparse. Unfortunately this fix
doesn't get rid of the warning.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reported-by: Jani Nikula <jani.nikula@intel.com>
Cc: Daniel Stone <daniels@collabora.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: dri-devel@lists.freedesktop.org
Fixes: 5488dc16

 ("drm: introduce pipe color correction properties")
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1458655833-19547-1-git-send-email-lionel.g.landwerlin@intel.com