f2fs: add an option to avoid unnecessary BUG_ONs

If you want to remove unnecessary BUG_ONs, you can just turn off F2FS_CHECK_FS
in your kernel config.

Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>
diff --git a/fs/f2fs/xattr.c b/fs/f2fs/xattr.c
index f685138..89d506d 100644
--- a/fs/f2fs/xattr.c
+++ b/fs/f2fs/xattr.c
@@ -372,7 +372,7 @@
 			alloc_nid_failed(sbi, new_nid);
 			return PTR_ERR(xpage);
 		}
-		BUG_ON(new_nid);
+		f2fs_bug_on(new_nid);
 	} else {
 		struct dnode_of_data dn;
 		set_new_dnode(&dn, inode, NULL, NULL, new_nid);