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/inode.c b/fs/f2fs/inode.c
index adc622c..2cf6962 100644
--- a/fs/f2fs/inode.c
+++ b/fs/f2fs/inode.c
@@ -78,6 +78,7 @@
 	if (check_nid_range(sbi, inode->i_ino)) {
 		f2fs_msg(inode->i_sb, KERN_ERR, "bad inode number: %lu",
 			 (unsigned long) inode->i_ino);
+		WARN_ON(1);
 		return -EINVAL;
 	}