screen_ui: Fix an issue in RTL locale detection.

The CL in [1] moved android.os.RecoverySystem to send the locale
argument in well-formed BCP 47 language tags (e.g. "en-US" instead of
"en_US"), with the matching changes to recovery code in [2]. However,
the one in ScreenRecoveryUI::SetLocale() was missed, which broke RTL
locale detection when using new format.

[1] commit 38715228 in platform/frameworks/base
[2] commit 2078b22e in platform/bootable/recovery

Test: Set the locale to "ar-EG". `Run graphics test` under recovery.
      Check the progress bar.
Test: Run recovery_unit_test on marlin.
Change-Id: I7c7f5e0725bfb096109c7192c19f3f008e8e47e3
diff --git a/tests/unit/screen_ui_test.cpp b/tests/unit/screen_ui_test.cpp
index ff8a35d..03e23ca 100644
--- a/tests/unit/screen_ui_test.cpp
+++ b/tests/unit/screen_ui_test.cpp
@@ -255,7 +255,7 @@
  protected:
   const std::string kTestLocale = "en-US";
   const std::string kTestRtlLocale = "ar";
-  const std::string kTestRtlLocaleWithSuffix = "ar_EG";
+  const std::string kTestRtlLocaleWithSuffix = "ar-EG";
 
   void SetUp() override {
     ui_ = std::make_unique<TestableScreenRecoveryUI>();