spi: mediatek: fix endian warnings

This patch fixes endian warnings detected by sparse:
- sparse: incorrect type in argument 1 (different base types)
	  expected unsigned int [unsigned] val
	  got restricted __le32 [usertype] <noident>
- sparse: incorrect type in argument 1 (different base types)
	  expected unsigned int [unsigned] val
	  got restricted __le32 [usertype] <noident>

Signed-off-by: Leilk Liu <leilk.liu@mediatek.com>
Signed-off-by: Mark Brown <broonie@kernel.org>