f2fs: should put the dnode when NEW_ADDR is detected

When get_dnode_of_data() in get_data_block() returns a successful dnode, we
should put the dnode.
But, previously, if its data block address is equal to NEW_ADDR, we didn't do
that, resulting in a deadlock condition.
So, this patch splits original error conditions with this case, and then calls
f2fs_put_dnode before finishing the function.

Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>