UBI: Fastmap: Fall back to scanning mode after ECC error

If we encounter an uncorrectable ECC error while scanning for the fastmap
UBI must not fail hard. Instead fall back to scanning mode.

Reported-by: Alexander Block <Alexander.Block@continental-corporation.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
Git-commit: 180a53577b809026af744e99a35b3a3a0056520b
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


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