buildroot

Revert "fs: use pseudo instead of fakeroot"

This reverts commit 8035ceb56cc3ba2541aba0d0ead3f29900d9e310.

Moving to pseudo brought a number of issues (and longer compilation time),
so lets stick with fakeroot now that the reported ubi issue has been worked
around.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>