FROMGIT: f2fs: don't sleep while grabing nat_tree_lock

This tries to fix priority inversion in the below condition resulting in
long checkpoint delay.

f2fs_get_node_info()
 - nat_tree_lock
  -> sleep to grab journal_rwsem by contention

                                     checkpoint
                                     - waiting for nat_tree_lock

In order to let checkpoint go, let's release nat_tree_lock, if there's a
journal_rwsem contention.

Signed-off-by: Daeho Jeong <daehojeong@google.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Bug: 191987855
(cherry picked from commit 2eeb0dce
 git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs.git

 dev)
Change-Id: I97ac4f9d3bde399ab4f17f5b3a6e949ae9b79f0f
Signed-off-by: Daeho Jeong <daehojeong@google.com>