virt: vbox: Fix guest capabilities mask check

commit 59d1d2e8 upstream.

Check the passed in capabilities against VMMDEV_GUEST_CAPABILITIES_MASK
instead of against VMMDEV_EVENT_VALID_EVENT_MASK.
This tightens the allowed mask from 0x7ff to 0x7.

Fixes: 0ba002bc

 ("virt: Add vboxguest driver for Virtual Box Guest integration")
Cc: stable@vger.kernel.org
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20200709120858.63928-3-hdegoede@redhat.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>