omap2_mcspi: Flush posted writes

mcspi_write_chconf0 is used to control rx/tx triggering.
Post-write flushing is needed to get the immediate effect.
Signed-off-by: NRoman Tereshonkov <roman.tereshonkov@nokia.com>
Signed-off-by: NGrant Likely <grant.likely@secretlab.ca>

drivers/spi/omap2_mcspi.c

@@ -204,6 +204,7 @@ static inline void mcspi_write_chconf0(const struct spi_device *spi, u32 val)
 
 	cs->chconf0 = val;
 	mcspi_write_cs_reg(spi, OMAP2_MCSPI_CHCONF0, val);
+	mcspi_read_cs_reg(spi, OMAP2_MCSPI_CHCONF0);
 }
 
 static void omap2_mcspi_set_dma_req(const struct spi_device *spi,