mm/swap: remove remaining _fn suffix

Remove remaining _fn suffix from cpu_fbatches handlers, which are already
self-explanatory.

Link: https://lkml.kernel.org/r/20240711021317.596178-5-yuzhao@google.com


Signed-off-by: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>