virt: vbox: core: fix all kernel-doc warnings

Use kernel-doc format for functions that have comments that begin
with "/**".
This prevents 26 kernel-doc warnings.
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20231222052521.14333-1-rdunlap@infradead.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>