[ssh_config] LogLevel ERROR to suppress warnings

Users don't like the key warning when using fx shell.

Change-Id: I9e5852a20c6d24b348bc7fc46891312d0d9bdffa
diff --git a/fuchsia/developer-keys/generate_ssh_config.sh b/fuchsia/developer-keys/generate_ssh_config.sh
index fcfbd66..3502ac8 100755
--- a/fuchsia/developer-keys/generate_ssh_config.sh
+++ b/fuchsia/developer-keys/generate_ssh_config.sh
@@ -15,4 +15,5 @@
   ControlPath /tmp/fuchsia-$USER-%r@%h:%p
   ServerAliveInterval 1
   ServerAliveCountMax 1
+  LogLevel ERROR
 EOF