ANDROID: fs: Export vfs_rmdir2

allmodconfig builds fail with

ERROR: "vfs_rmdir2" undefined!

Export the missing function.

Change-Id: I983d327e59fd34e0484f3c54d925e97d3905c19c
Fixes: f9cb61dcb00c ("ANDROID: sdcardfs: User new permission2 functions")
Signed-off-by: Guenter Roeck <groeck@chromium.org>
(cherry picked from commit 4c7fc336f6e3ec34af2c6931fce4d496f560da90)
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>