mei: vsc: Event notifier fixes

vsc_tp_register_event_cb() can race with vsc_tp_thread_isr(), add a mutex
to protect against this.

Fixes: 566f5ca9 ("mei: Add transport driver for IVSC device")
Signed-off-by: Hans de Goede <hansg@kernel.org>
Link: https://lore.kernel.org/r/20250623085052.12347-7-hansg@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>