f2fs: check lower bound nid value in check_nid_range

This patch add lower bound verification for nid in check_nid_range, so nids
reserved like 0, node, meta passed by caller could be checked there.

And then check_nid_range could be used in f2fs_nfs_get_inode for simplifying
code.

Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index b2b1863..8f96d93 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -689,9 +689,7 @@
 	struct f2fs_sb_info *sbi = F2FS_SB(sb);
 	struct inode *inode;
 
-	if (unlikely(ino < F2FS_ROOT_INO(sbi)))
-		return ERR_PTR(-ESTALE);
-	if (unlikely(ino >= NM_I(sbi)->max_nid))
+	if (check_nid_range(sbi, ino))
 		return ERR_PTR(-ESTALE);
 
 	/*