spi: Add missing kerneldoc description for parameter

Commit ca5d24854210 ("spi: Add THIS_MODULE to spi_driver in SPI core")
adds the new __spi_register_driver() function, but keeps the kerneldoc
for the spi_register_driver() function in place and forgets to add the
description for the new owner parameter.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi.c

@@ -376,6 +376,7 @@ static void spi_drv_shutdown(struct device *dev)
 
 /**
  * __spi_register_driver - register a SPI driver
+ * @owner: owner module of the driver to register
  * @sdrv: the driver to register
  * Context: can sleep
  *