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: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1488280303-9323-1-git-send-email-jani.nikula@intel.com
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 7115265..48b34a9 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/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 {
diff --git a/drivers/gpu/drm/i915/intel_device_info.c b/drivers/gpu/drm/i915/intel_device_info.c
index 2e1fd85..9fc6ab7 100644
--- a/drivers/gpu/drm/i915/intel_device_info.c
+++ b/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>";