wifi: iwlwifi: Implement settime64 as stub for MVM/MLD PTP

wifi: iwlwifi: Implement settime64 as stub for MVM/MLD PTP

Since commit dfb073d32cac ("ptp: Return -EINVAL on ptp_clock_register if
required ops are NULL"), PTP clock registered through ptp_clock_register
is required to have ptp_clock_info.settime64 set, however, neither MVM
nor MLD's PTP clock implementation sets it, resulting in warnings when
the interface starts up, like

WARNING: drivers/ptp/ptp_clock.c:325 at ptp_clock_register+0x2c8/0x6b8, CPU#1: wpa_supplicant/469
CPU: 1 UID: 0 PID: 469 Comm: wpa_supplicant Not tainted 6.18.0+ #101 PREEMPT(full)
ra: ffff800002732cd4 iwl_mvm_ptp_init+0x114/0x188 [iwlmvm]
ERA: 9000000002fdc468 ptp_clock_register+0x2c8/0x6b8
iwlwifi 0000:01:00.0: Failed to register PHC clock (-22)

I don't find an appropriate firmware interface to implement settime64()
for iwlwifi MLD/MVM, thus instead create a stub that returns
-EOPTNOTSUPP only, suppressing the warning and allowing the PTP clock to
be registered.

Reported-by: Nathan Chancellor <nathan@kernel.org>
Closes: https://lore.kernel.org/all/20251108044822.GA3262936@ax162/
Signed-off-by: Yao Zi <ziyao@disroot.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Simon Horman <horms@kernel.org>
tested-by: damian Tometzki damian@riscv-rocks.de
Tested-by: Oliver Hartkopp <socketcan@hartkopp.net>
Acked-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://patch.msgid.link/20251204123204.9316-1-ziyao@disroot.org
Signed-off-by: Johannes Berg <johannes.berg@intel.com>