spi: npcm-fiu: Fix typo ("npxm")

The platform is called NPCM, not NPXM.

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Link: https://lore.kernel.org/r/20220306142312.109017-1-j.neuschaefer@gmx.net


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