Switch reported frequency to 400MHz

This is the actual frequency we're using (not the maximum potential
frequency). At 500MHz the driver complains that GPU frequency
calibration is incorrect.

Change-Id: Ie64b6adca6b746738e12b57648ab57fca07f8d56
diff --git a/services/system/fuchsia/sysconfig.cc b/services/system/fuchsia/sysconfig.cc
index ad320ed..da92a8e 100644
--- a/services/system/fuchsia/sysconfig.cc
+++ b/services/system/fuchsia/sysconfig.cc
@@ -198,7 +198,7 @@
 	sys_info->physHeapConfig[0].psMemFuncs = &sys_info->physHeapFuncs;
 	sys_info->physHeapConfig[0].hPrivData = NULL;
 
-	constexpr uint32_t kRgxHwCoreClockSpeed = 500'000'000;
+	constexpr uint32_t kRgxHwCoreClockSpeed = 400'000'000;
 	constexpr uint32_t kRgxActivePowerLatencyMs = 50;
 	/*
          * Setup RGX specific timing data