UBI: Fastmap: Set used_ebs only for static volumes

If we set it for dynamic ones we might confuse various self checks.

Signed-off-by: Richard Weinberger <richard@nod.at>
Git-commit: 42dd3cdcd6b5671ebedc3df76ca8dcc3473bcc67
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Nikhilesh Reddy <reddyn@codeaurora.org>