ice: Zero out the PTP control PF pointer at ice_adapter cleanup

Zero out the ctrl_pf pointer in ice_adapter when the control PF is removed.
This prevents potential dangling pointer dereference when accessing
PTP-related structures from other PFs of the same adapter.

Fixes: e800654e85b5b ("ice: Use ice_adapter for PTP shared data instead of auxdev")
Signed-off-by: Sergey Temerkhanov <sergey.temerkhanov@intel.com>
Reported-by: Frederick Lawler <fred@cloudflare.com>
Closes: https://lkml.indiana.edu/2507.3/01388.html
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Reviewed-by: Arkadiusz Kubalewski <arkadiusz.kubalewski@intel.com>
Tested-by: Frederick Lawler <fred@cloudflare.com>