spi: fsl_dspi: rename num-cs to spi-num-chipselects

The official devicetree bindings specifies spi-num-chipselects as the
name. Use it.

Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>
diff --git a/drivers/spi/fsl_dspi.c b/drivers/spi/fsl_dspi.c
index 23d812f..62444e4 100644
--- a/drivers/spi/fsl_dspi.c
+++ b/drivers/spi/fsl_dspi.c
@@ -586,8 +586,9 @@
 	if (fdtdec_get_bool(blob, node, "big-endian"))
 		plat->flags |= DSPI_FLAG_REGMAP_ENDIAN_BIG;
 
-	plat->num_chipselect =
-		fdtdec_get_int(blob, node, "num-cs", FSL_DSPI_MAX_CHIPSELECT);
+	plat->num_chipselect = fdtdec_get_int(blob, node,
+					      "spi-num-chipselects",
+					      FSL_DSPI_MAX_CHIPSELECT);
 
 	addr = dev_read_addr(bus);
 	if (addr == FDT_ADDR_T_NONE) {