docs: filesystems: vfs: Remove space before tab

Currently the file has a bunch of spaces before tabspaces.  This is a
nuisance when patching the file because they show up whenever we touch
these lines.  Let's just fix them all now in preparation for doing the
RST conversion.

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