ratectrl_rtc.h: quiet MSVC int64_t->int conv warning

target_bandwidth is int64_t, but layer_target_bitrate[0] is an int. this
is safe in the only place it's set because target_bandwidth defaults to
1000. target_bandwidth is later used to populate the cpi's target, which
is an unsigned int so there may be further fixes/cleanups that can be
done.

Change-Id: I35dbaa2e55a0fca22e0e2680dcac9ea4c6b2815a
diff --git a/vp9/ratectrl_rtc.h b/vp9/ratectrl_rtc.h
index a30ec1d..f219f24 100644
--- a/vp9/ratectrl_rtc.h
+++ b/vp9/ratectrl_rtc.h
@@ -50,7 +50,7 @@
     vp9_zero(ts_rate_decimator);
     scaling_factor_num[0] = 1;
     scaling_factor_den[0] = 1;
-    layer_target_bitrate[0] = target_bandwidth;
+    layer_target_bitrate[0] = static_cast<int>(target_bandwidth);
     max_quantizers[0] = max_quantizer;
     min_quantizers[0] = min_quantizer;
     ts_rate_decimator[0] = 1;