spi: stm32: replace st, spi-midi with st, spi-midi-ns to fit bindings

This patch fixes the optional dt property used to set master inter-data
idleness.

Signed-off-by: Amelie Delaunay <amelie.delaunay@st.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-stm32.c

@@ -582,7 +582,7 @@ static int stm32_spi_prepare_msg(struct spi_master *master,
 
 	/* SPI slave device may need time between data frames */
 	spi->cur_midi = 0;
-	if (np && !of_property_read_u32(np, "st,spi-midi", &spi->cur_midi))
+	if (np && !of_property_read_u32(np, "st,spi-midi-ns", &spi->cur_midi))
 		dev_dbg(spi->dev, "%dns inter-data idleness\n", spi->cur_midi);
 
 	if (spi_dev->mode & SPI_CPOL)