nilfs2: correct return value kernel-doc descriptions for sufile

Similar to the previous changes to fix return value descriptions, this
fixes the format of the return value descriptions of functions for
sufile-related functions, eliminating a dozen warnings emitted by the
kernel-doc script.

Link: https://lkml.kernel.org/r/20250110010530.21872-4-konishi.ryusuke@gmail.com


Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Cc: "Brian G ." <gissf1@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>