UBIFS: improve journal head debugging prints

Convert the journal head integer into the head name when printing
debugging information.

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

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

diff --cc fs/ubifs/debug.h
Simple merge

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

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

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