[tools] Update build command when needed for fidl-format

The old build command is no longer working. I believe this change
addresses the original intent.

Test: tested locally to confirm it works

Change-Id: Ib097f5e713b4794a66daaf9332da2db2c0158cc1
diff --git a/tools/devshell/contrib/format-code b/tools/devshell/contrib/format-code
index 8675861..6205c1b 100755
--- a/tools/devshell/contrib/format-code
+++ b/tools/devshell/contrib/format-code
@@ -170,7 +170,7 @@
   if [[ ${file} =~ .*\.fidl ]]; then
     if [[ ! -x "${FIDL_BIN}" ]]; then
        printf "fidl-format not found: attempting to build it\n"
-       fx-command-run build-zircon -T
+       fx-command-run build system/fidl:tools
        break
      fi
   fi