UBIFS: switch to I/O helpers

Switch the rest of direct UBI calls to UBIFS helper functions.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

diff --cc fs/ubifs/log.c
Simple merge

diff --cc fs/ubifs/lpt.c
Simple merge

diff --cc fs/ubifs/recovery.c
Simple merge

diff --cc fs/ubifs/sb.c
Simple merge

diff --cc fs/ubifs/super.c
Simple merge