Specify LOCAL_INSTALLED_MODULE_STEM for prebuilt_etc.

Otherwise the recovery variant gets installed with `.recovery` suffix.

Bug: 112780007
Test: Build with the mke2fs.conf change (using Android.bp to install
      mke2fs.conf). Check the installed filenames (under normal boot and
      recovery both).
Change-Id: I882be2fa07b530667a2dafc2bfe18730a42c4c08