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/arch/x86/cpu/apollolake/spl.c b/arch/x86/cpu/apollolake/spl.c
index 4110619..3a1588b 100644
--- a/arch/x86/cpu/apollolake/spl.c
+++ b/arch/x86/cpu/apollolake/spl.c
@@ -92,7 +92,7 @@
 {
 	if (CONFIG_IS_ENABLED(OF_PLATDATA) &&
 	    !CONFIG_IS_ENABLED(OF_PLATDATA_PARENT)) {
-		struct dm_spi_slave_platdata *plat;
+		struct dm_spi_slave_plat *plat;
 		struct udevice *spi;
 		int ret;