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 <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Christian Brauner <[e-mail]>

Documentation/filesystems/files.rst

···
 in get_file_rcu() and __files_get_rcu().
 
 In addition, it isn't possible to access or check fields in struct file
-without first aqcuiring a reference on it under rcu lookup. Not doing
+without first acquiring a reference on it under rcu lookup. Not doing
 that was always very dodgy and it was only usable for non-pointer data
 in struct file. With SLAB_TYPESAFE_BY_RCU it is necessary that callers
 either first acquire a reference or they must hold the files_lock of the