virtiofsd: Directory for PID file hardcoded

With QEMU 6.0.0, -o vhost_user_socket=/tmp/vhostqemu, mentioned on Standalone virtio-fs usage, does not work, and using the switch --socket-path listed in the help/usage, gives the error below.

$ /pkg/qemu-6.0.0-0/libexec/virtiofsd --socket-path=/tmp/vhostqemu -o source=virtiofsd -o cache=always
fv_socket_lock: Failed to create directory /pkg/qemu-6.0.0-0/libexec/../var/run/virtiofsd: Permission denied