package/mtd: add upstream patch that fixes ubiformat return code

ubiformat returns 255 even on successful format actions, since the upgrade
of mtd-utils to version 2.1.1.

Backport an upstream patch that fixes this issue. No new release is made
yet.

Signed-off-by: Thomas De Schampheleire <thomas.de_schampheleire@nokia.com>
[yann.morin.1998@free.fr: make it explicit it's a backported patch]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>