Set correct style for AlertDialog

Otherwise it inherits the incorrect text color

<item name="android:textColorPrimary">@color/incall_call_banner_text_color</item>

from Theme.InCallScreen.

Bug: 19796458
Change-Id: I4e86f4a114b39d8c2060638eb05142791385c8e9
diff --git a/InCallUI/res/values/styles.xml b/InCallUI/res/values/styles.xml
index dba7cc3..11d6362 100644
--- a/InCallUI/res/values/styles.xml
+++ b/InCallUI/res/values/styles.xml
@@ -85,6 +85,7 @@
         <item name="android:popupMenuStyle">@style/InCallPopupMenuStyle</item>
         <item name="android:actionBarStyle">@style/InCallActionBarStyle</item>
         <item name="android:buttonStyleToggle">@style/InCallCompoundButton</item>
+        <item name="android:alertDialogTheme">@android:style/Theme.Material.Light.Dialog.Alert</item>
     </style>
 
     <style name="InCallPopupMenuStyle" parent="@android:style/Theme.Material.Light">