docs: filesystems: fix typo in docs

This patch resolves a spelling error in the filesystem documentation.

It is submitted as part of my application to the "Linux Kernel Bug
Fixing Spring Unpaid 2024" mentorship program of the Linux Kernel
Foundation.

Signed-off-by: Vincenzo Mezzela <vincenzo.mezzela@gmail.com>
Link: https://lore.kernel.org/r/20240208162032.109184-1-vincenzo.mezzela@gmail.com


Signed-off-by: Christian Brauner <brauner@kernel.org>