gpu/host1x: bus: Add missing description for 'driver'

Fixes the following W=1 kernel build warning(s):

drivers/gpu/host1x/bus.c:40: warning: Function parameter or member 'driver' not described in 'host1x_subdev_add'

Cc: Thierry Reding <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Signed-off-by: Lee Jones <[e-mail]>
Acked-by: Thierry Reding <[e-mail]>
Signed-off-by: Sam Ravnborg <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/host1x/bus.c

···
 /**
  * host1x_subdev_add() - add a new subdevice with an associated device node
  * @device: host1x device to add the subdevice to
+ * @driver: host1x driver containing the subdevices
  * @np: device node
  */
 static int host1x_subdev_add(struct host1x_device *device,