docs: filesystems: vfs: Use 72 character column width

In preparation for conversion to RST format use the kernels favoured
documentation column width.  If we are going to do this we might as well
do it thoroughly.  Just do the paragraphs (not the indented stuff), the
rest will be done during indentation fix up patch.

This patch is whitespace only, no textual changes.

Use 72 character column width for all paragraph sections.

Tested-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Tobin C. Harding <tobin@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>