drm/i915: convert a few more E->dev_private to to_i915(E)

drm/i915: convert a few more E->dev_private to to_i915(E)

Also remove some redundant dev and dev_priv locals

Signed-off-by: Dave Gordon <david.s.gordon@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1467626365-29871-1-git-send-email-david.s.gordon@intel.com
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1467628477-25379-2-git-send-email-chris@chris-wilson.co.uk