drm/i915: Fix read outside array bounds in restoring the SWF10 range.

dev_priv->saveSWF1 is a 16 element array, but this reads up to index 22,
and restored values from the wrong registers.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Signed-off-by: Eric Anholt <eric@anholt.net>