f2fs: fix wrong condition check to trigger f2fs_sync_fs

If there is not enough available memory, we need to trigger f2fs_sync_fs.

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 42607a6..11e4b5c 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -290,7 +290,7 @@
 	/* check the # of cached NAT entries and prefree segments */
 	if (try_to_free_nats(sbi, NAT_ENTRY_PER_BLOCK) ||
 			excess_prefree_segs(sbi) ||
-			available_free_memory(sbi, INO_ENTRIES))
+			!available_free_memory(sbi, INO_ENTRIES))
 		f2fs_sync_fs(sbi->sb, true);
 }