Fix Settings manifest pointing to old class namespace

The string declaring the right fragment was never updated to the new
namespace.

Change-Id: I35809f2f35dbf290deeb69d1bc672b86f8d5a752
Fixes: 63677809
Test: make SettingsUnitTests && \
adb install -r out/target/product/<device>/data/app/SettingsUnitTests/SettingsUnitTests.apk && \
adb shell am instrument -w -e class \
com.android.settings.dream.DreamSettingsLaunchTest\
com.android.settings.tests.unit/android.support.test.runner.AndroidJUnitRunner