um: virtio_uml: use raw spinlock

This is needed because at least in time-travel the code
can be called directly from the deep architecture and
IRQ handling code.

Link: https://patch.msgid.link/20250110125550.32479-7-johannes@sipsolutions.net


Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Richard Weinberger <richard@nod.at>