Don't call OpenModeToAndroid in GBACore

`OpenModeToAndroid("r")` is conceptually wrong, since we're opening a
binary file. It should be either `OpenModeToAndroid("rb")` or just
`"r"`. But either way it evaluates to `"r"`, so this doesn't affect
behavior.

Source/Core/Core/HW/GBACore.cpp

@@ -134,7 +134,7 @@ static VFile* OpenReadOnlyFile(const char* path)
 {
 #ifdef ANDROID
   if (IsPathAndroidContent(path))
-    return VFileFromFD(OpenAndroidContent(path, OpenModeToAndroid("r")));
+    return VFileFromFD(OpenAndroidContent(path, "r"));
 #endif
   return VFileOpen(path, O_RDONLY);
 }