EOPNOTSUPP is widely used as error number indicating operation is
not supported in syscall, and ENOTSUPP was defined and only used
for NFSv3 protocol, so use EOPNOTSUPP instead.

Fixes: 0a2aa8fb ("f2fs: refactor __exchange_data_block for speed up")
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>