UBI: Fastmap: Fix fastmap usage in ubi_volume_notify()

There is no need to switch to ro mode if ubi_update_fastmap() fails.
Also get rid of the ifdef.

Signed-off-by: Richard Weinberger <richard@nod.at>
Reviewed-by: Tanya Brokhman <tlinder@codeaurora.org>
Git-commit: 84b678f497c6eda650f0640bd7cf165e2c1acb49
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


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