drm/i915: Account for the size of the chroma plane for the rotated gtt view

The size of the rotated ggtt mapping ought to include the size of the
chroma plane as well. Not a huge deal since we don't expose NV12 (or any
pother planar format for that matter) yet.

Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Fixes: 89e3e142 ("drm/i915: Support NV12 in rotated GGTT mapping")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1455569699-27905-2-git-send-email-ville.syrjala@linux.intel.com


Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>