Btrfs: fix inode leak on kmalloc failure in tree-log.c

In tree-log.c:replay_one_name(), if memory allocation for
the name fails, ensure we iput the dir inode we got before
before we return.

Signed-off-by: Filipe David Borba Manana <fdmanana@gmail.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>