drm/i915: fix regression after clock gating init split

During the refactoring in revision 6067aaea,
the intel_enable_clock_gating was split up into several functions that are
then called indirectly. However, which function to call was not specified for
the IS_PINEVIEW() case. This patch specifies the correct gating function.

Signed-off-by: Jason Stubbs <jasonbstubbs@gmail.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Keith Packard <keithp@keithp.com>