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>

fs/f2fs/file.c

@@ -296,7 +296,7 @@ static int truncate_blocks(struct inode *inode, u64 from)
 		count = ADDRS_PER_BLOCK;
 
 	count -= dn.ofs_in_node;
-	BUG_ON(count < 0);
+	f2fs_bug_on(count < 0);
 
 	if (dn.ofs_in_node || IS_INODE(dn.node_page)) {
 		truncate_data_blocks_range(&dn, count);