Fix --bazel-mode-staging flag.

It was assigning --bazel-mode-staging to cmdlineArgs.BazelMode, which
looks wrong.

Test: presubmits
Change-Id: I24b087977fc6861eef3a1c30e58d9bf42a344c52
diff --git a/cmd/soong_build/main.go b/cmd/soong_build/main.go
index 1e356e5..2cea5a5 100644
--- a/cmd/soong_build/main.go
+++ b/cmd/soong_build/main.go
@@ -91,7 +91,7 @@
 	flag.StringVar(&cmdlineArgs.OutFile, "o", "build.ninja", "the Ninja file to output")
 	flag.BoolVar(&cmdlineArgs.EmptyNinjaFile, "empty-ninja-file", false, "write out a 0-byte ninja file")
 	flag.BoolVar(&cmdlineArgs.BazelMode, "bazel-mode", false, "use bazel for analysis of certain modules")
-	flag.BoolVar(&cmdlineArgs.BazelMode, "bazel-mode-staging", false, "use bazel for analysis of certain near-ready modules")
+	flag.BoolVar(&cmdlineArgs.BazelModeStaging, "bazel-mode-staging", false, "use bazel for analysis of certain near-ready modules")
 	flag.BoolVar(&cmdlineArgs.BazelModeDev, "bazel-mode-dev", false, "use bazel for analysis of a large number of modules (less stable)")
 
 	// Flags that probably shouldn't be flags of soong_build but we haven't found