spi: fsl-lib: Fix memory leak of pinfo

of_mpc8xxx_spi_probe() allocates memory for pinfo but the memory is not freed
anywhere. of_mpc8xxx_spi_probe() is called in .probe() and pinfo should be
freed in .remove(), so convert kzalloc to devm_kzalloc to fix the memory leak.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Mark Brown <broonie@linaro.org>