jbd2: remove bunch of empty lines with jbd2 debug

See following dmesg output with jbd2 debug enabled:

...(start_this_handle, 313): New handle 00000000c88d6ceb going live.

...(start_this_handle, 383): Handle 00000000c88d6ceb given 53 credits (total 53, free 32681)

...(do_get_write_access, 838): journal_head 0000000002856fc0, force_copy 0

...(jbd2_journal_cancel_revoke, 421): journal_head 0000000002856fc0, cancelling revoke

We have an extra line with every messages, this is a waste of buffer,
we can fix it by removing "\n" in the caller or remove it in
the __jbd2_debug(), i checked every jbd2_debug() passed '\n' explicitly.

To avoid more lines, let's remove it inside __jbd2_debug().

Signed-off-by: Wang Shilong <wshilong@ddn.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jan Kara <jack@suse.cz>