mfd: intel_soc_pmic_core: Terminate panel control GPIO lookup table correctly

GPIO lookup tables are supposed to be zero terminated. Let's do that
and avoid accidentally walking off the end.

Cc: Shobhit Kumar <shobhit.kumar@intel.com>
Cc: Samuel Ortiz <sameo@linux.intel.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Alexandre Courbot <gnurou@gmail.com>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Lee Jones <lee.jones@linaro.org>
Cc: stable@vger.kernel.org
Fixes: 61dd2ca2

 ("mfd: intel_soc_pmic_core: Add lookup table for Panel Control as GPIO signal")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Thierry Reding <treding@nvidia.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1461353935-8078-1-git-send-email-ville.syrjala@linux.intel.com