docs: f2fs: fix text alignment

The docs build was generating this warning:

  Documentation/filesystems/f2fs.rst:306: WARNING: Block quote ends without a blank line; unexpected unindent.

Remove the extra white space that was confusing sphinx.

Fixes: 151b1982

 (f2fs: compress: add nocompress extensions support)
Signed-off-by: Fengnan Chang <changfengnan@vivo.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20211023025833.216030-1-changfengnan@vivo.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>