dm: Use access methods for dev/uclass private data

Most drivers use these access methods but a few do not. Update them.

In some cases the access is not permitted, so mark those with a FIXME tag
for the maintainer to check.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Pratyush Yadav <p.yadav@ti.com>
diff --git a/drivers/spi/designware_spi.c b/drivers/spi/designware_spi.c
index 4fa4585..5ede00d 100644
--- a/drivers/spi/designware_spi.c
+++ b/drivers/spi/designware_spi.c
@@ -155,7 +155,7 @@
 
 static int dw_spi_of_to_plat(struct udevice *bus)
 {
-	struct dw_spi_plat *plat = bus->plat;
+	struct dw_spi_plat *plat = dev_get_plat(bus);
 
 	plat->regs = dev_read_addr_ptr(bus);
 
@@ -478,7 +478,7 @@
 
 static int dw_spi_set_speed(struct udevice *bus, uint speed)
 {
-	struct dw_spi_plat *plat = bus->plat;
+	struct dw_spi_plat *plat = dev_get_plat(bus);
 	struct dw_spi_priv *priv = dev_get_priv(bus);
 	u16 clk_div;