spi: pxa2xx: Return error codes from pxa2xx_spi_init_pdata()

For better understanding what's going on on error path,
return distinguished error codes instead of NULL pointer.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20200224154556.11627-1-andriy.shevchenko@linux.intel.com


Signed-off-by: Mark Brown <broonie@kernel.org>