spi: npcm-pspi: Fix wrong priv pointer

In npcm_pspi_probe(), current code set platform_set_drvdata(pdev, master);
so in npcm_pspi_remove() platform_get_drvdata(pdev) will return pointer to
master rather than priv. Fix it.

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