Fix sparse warning:

drivers/gpu/drm/i915/intel_device_info.c:195:31: warning: Variable
length array is used.

In truth the array does have constant length, but sparse is too dumb to
realize. This is a bit ugly, but silence the warning no matter what.

Fixes: 91bedd34 ("drm/i915/bdw: Check for slice, subslice and EU count for BDW")
Reviewed-by: NJoonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1475574853-4178-1-git-send-email-jani.nikula@intel.com