drm/virtio: allocate fences with GFP_KERNEL

It was changed to GFP_ATOMIC in commit ec2f0577 (add & use
virtio_gpu_queue_fenced_ctrl_buffer) because the allocation happened
with a spinlock held.  That was no longer true after commit
9fdd90c0 (add virtio_gpu_alloc_fence()).

Signed-off-by: Chia-I Wu <olvaffe@gmail.com>
Reviewed-by: Robert Foss <robert.foss@collabora.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20190429221021.159784-1-olvaffe@gmail.com


Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Gustavo Padovan <gustavo.padovan@collabora.com>
Cc: Robert Foss <robert.foss@collabora.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>