dm: treewide: Rename ..._platdata variables to just ..._plat

Try to maintain some consistency between these variables by using _plat as
a suffix for them.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/spi/stm32_spi.c b/drivers/spi/stm32_spi.c
index d2c2262..720103d 100644
--- a/drivers/spi/stm32_spi.c
+++ b/drivers/spi/stm32_spi.c
@@ -362,7 +362,7 @@
 			  const void *dout, void *din, unsigned long flags)
 {
 	struct udevice *bus = dev_get_parent(slave);
-	struct dm_spi_slave_platdata *slave_plat;
+	struct dm_spi_slave_plat *slave_plat;
 	struct stm32_spi_priv *priv = dev_get_priv(bus);
 	u32 sr;
 	u32 ifcr = 0;