spi/doc: spi_master_put must be followed up by kfree

 *

 * The caller is responsible for assigning the bus number and initializing

 * the master's methods before calling spi_register_master(); and (after errors

 * adding the device) calling spi_master_put() to prevent a memory leak.

 * adding the device) calling spi_master_put() and kfree() to prevent a memory

 * leak.

 */

struct spi_master *spi_alloc_master(struct device *dev, unsigned size)

{