spi: dw: Convert dw_spi::num_cs to u32

Number of native chip-select lines is either retrieved from the "num-cs"
DT-property or auto-detected in the generic DW APB/AHB SSI probe method.
In the former case the property is supposed to be of the "u32" size.
Convert the field type to being u32 then to be able to drop the temporary
variable afterwards.
Signed-off-by: Serge Semin <fancer.lancer@gmail.com>
Reviewed-by: Andy Shevchenko <andy@kernel.org>
Link: https://lore.kernel.org/r/20240424150657.9678-4-fancer.lancer@gmail.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-dw.h

@@ -164,8 +164,8 @@ struct dw_spi {
 	u32			max_freq;	/* max bus freq supported */
 
 	u32			reg_io_width;	/* DR I/O width in bytes */
+	u32			num_cs;		/* chip select lines */
 	u16			bus_num;
-	u16			num_cs;		/* supported slave numbers */
 	void (*set_cs)(struct spi_device *spi, bool enable);
 
 	/* Current message transfer state info */