dm: mmc: Use cfg directly in mmc_bind()

This small change tidies up the code slightly.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/mmc/mmc.c b/drivers/mmc/mmc.c
index b7c936c..94f19ad 100644
--- a/drivers/mmc/mmc.c
+++ b/drivers/mmc/mmc.c
@@ -1557,7 +1557,7 @@
 	bdesc->removable = 1;
 
 	/* setup initial part type */
-	bdesc->part_type = mmc->cfg->part_type;
+	bdesc->part_type = cfg->part_type;
 	mmc->dev = dev;
 
 	return 0;