drm/i915: use BUILD_BUG_ON to ensure platform name has been set up

Leave the runtime check in place in case the platform variable itself
comes from bogus sources.
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1488280303-9323-1-git-send-email-jani.nikula@intel.com

drivers/gpu/drm/i915/i915_drv.h

@@ -889,6 +889,7 @@ enum intel_platform {
 	INTEL_BROXTON,
 	INTEL_KABYLAKE,
 	INTEL_GEMINILAKE,
+	INTEL_MAX_PLATFORMS
 };
 
 struct intel_device_info {

drivers/gpu/drm/i915/intel_device_info.c

@@ -56,6 +56,8 @@ static const char * const platform_names[] = {
 
 const char *intel_platform_name(enum intel_platform platform)
 {
+	BUILD_BUG_ON(ARRAY_SIZE(platform_names) != INTEL_MAX_PLATFORMS);
+
 	if (WARN_ON_ONCE(platform >= ARRAY_SIZE(platform_names) ||
 			 platform_names[platform] == NULL))
 		return "<unknown>";