When passing UBIFS parameters via kernel command line, the
sync option will be passed to UBIFS as a string, not as an
MS_SYNCHRONOUS flag. Teach UBIFS interpreting this flag.
Reported-by: NAurélien GÉRÔME <ag@debian.org>
Signed-off-by: NArtem Bityutskiy <Artem.Bityutskiy@nokia.com>