virt: vbox: Do not use wait_event_interruptible when called from kernel context

Do not use wait_event_interruptible when vbg_hgcm_call() gets called from
kernel-context, such as it being called by the vboxsf filesystem code.

This fixes some filesystem related system calls on shared folders
unexpectedly failing with -EINTR.

Fixes: 0532a1b0

 ("virt: vbox: Implement passing requestor info to the host for VirtualBox 6.0.x")
Reported-by: Ludovic Pouzenc <bugreports@pouzenc.fr>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20210121150754.147598-1-hdegoede@redhat.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>