FROMLIST: f2fs: sanity check size of nat and sit cache

Make sure number of entires doesn't exceed max journal size.

Cc: stable@vger.kernel.org
Signed-off-by: Jin Qian <jinqian@android.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

(url https://sourceforge.net/p/linux-f2fs/mailman/message/35872032)
Bug: 36819470
Change-Id: I94ad46eb3586cfcdd5f477a6caa2244b7d05da56