virt: vbox: Fix some comments which talk about the "session spinlock"

The session lock is a mutex, not a spinlock, fix the comments to match.

Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20200709120858.63928-9-hdegoede@redhat.com


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