f2fs: fix to check return value in f2fs_insert_range()

In f2fs_insert_range(), it missed to check return value of
filemap_write_and_wait_range(), fix it.

Meanwhile, just return error number once __exchange_data_block()
fails.

Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>