spi/mpc52xx: Fix error handling in probe function

The call to spi_master_put() is needed to free device memory. It must be called
after spi_alloc_master, and must only be called after the device memory is no
longer used.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>