drm/i915: fix the power well ID for always on wells

drm/i915: fix the power well ID for always on wells

lookup_power_well() expects uniq power well IDs, but atm we have
uninitialized IDs which would clash with those power wells with a 0
ID. This wasn't a problem so far since nothing looked up such a power
well, but an upcoming patch will (Misc IO for SKL), so fix this up on
platforms where this matters.

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Patrik Jakobsson <patrik.jakobsson@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1446657859-9598-2-git-send-email-imre.deak@intel.com