documentation/filesystems: fix spelling mistakes

documentation/filesystems: fix spelling mistakes

Corrected the following spelling mistakes,
based on the suggestions by codespell:

1. Optionaly   -> Optionally
2. prefereable -> preferable
3. peformance  -> performance
4. ontext      -> context
5. failuer     -> failure
6. poiners     -> pointers
7. realtively  -> relatively
8. uptream     -> upstream

Signed-off-by: Ritvik Gupta <ritvikfoss@gmail.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20250210043937.30952-1-ritvikfoss@gmail.com