jbd2: Unify log messages in jbd2 code

Some jbd2 code prints out kernel messages with "JBD2: " prefix, at the
same time other jbd2 code prints with "JBD: " prefix. Unify the prefix
to "JBD2: ".

Signed-off-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --cc fs/jbd2/commit.c
Simple merge

diff --cc fs/jbd2/journal.c
Simple merge

diff --cc fs/jbd2/recovery.c
Simple merge

diff --cc fs/jbd2/transaction.c
Simple merge