fs/reiserfs/journal.c: fix sparse context imbalance warning

Merge conditional unlock/lock in the same condition to avoid sparse
warning:

  fs/reiserfs/journal.c:703:36: warning: context imbalance in 'add_to_chunk' - unexpected unlock

Signed-off-by: Fabian Frederick <fabf@skynet.be>
Cc: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>