perf/x86/amd: Use try_cmpxchg() in events/amd/{un,}core.c

Replace this pattern in events/amd/{un,}core.c:

    cmpxchg(*ptr, old, new) == old

... with the simpler and faster:

    try_cmpxchg(*ptr, &old, new)

The x86 CMPXCHG instruction returns success in the ZF flag, so this change
saves a compare after the CMPXCHG.

No functional change intended.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20240425101708.5025-1-ubizjak@gmail.com