tty: serdev: core: Provide missing description for 'owner'

tty: serdev: core: Provide missing description for 'owner'

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

 drivers/tty/serdev/core.c: In function ‘serdev_controller_remove’:
 drivers/tty/serdev/core.c:811: warning: Function parameter or member 'owner' not described in '__serdev_device_driver_register'

Cc: Rob Herring <robh@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jirislaby@kernel.org>
Cc: linux-serial@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20201104193549.4026187-3-lee.jones@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>