epoll: use try_cmpxchg in list_add_tail_lockless

Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in
list_add_tail_lockless.  x86 CMPXCHG instruction returns success in ZF
flag, so this change saves a compare after cmpxchg (and related move
instruction in front of cmpxchg).

No functional change intended.

Link: https://lkml.kernel.org/r/20220714173255.12987-1-ubizjak@gmail.com


Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>