drm/i915: Really calculate the cursor ddb based on the highest enabled wm level

drm/i915: Really calculate the cursor ddb based on the highest enabled wm level

I added the loop but neglected to actually pass the level to the
function. So we were just looping 8 times calculating the exact
same thing every time.

Fixes: 5c6b4490b51b ("drm/i915: Allocate enough DDB for the cursor")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190321175128.32178-1-ville.syrjala@linux.intel.com
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>