ANDROID: GKI: fs.h: add Android ABI padding to struct file

Try to mitigate potential future driver core api changes by adding
padding to struct file;

Bug: 151154716
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: Iba08ecfbd9cf365fe867cb57dbadf2eea00eaf0c