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/mtd/spi/sandbox.c b/drivers/mtd/spi/sandbox.c
index 5027439..740bd75 100644
--- a/drivers/mtd/spi/sandbox.c
+++ b/drivers/mtd/spi/sandbox.c
@@ -124,7 +124,7 @@
 	const struct flash_info *data;
 	struct sandbox_spi_flash_plat_data *pdata = dev_get_plat(dev);
 	struct sandbox_state *state = state_get_current();
-	struct dm_spi_slave_platdata *slave_plat;
+	struct dm_spi_slave_plat *slave_plat;
 	struct udevice *bus = dev->parent;
 	const char *spec = NULL;
 	struct udevice *emul;