mmc: Drop duplicate dm.h inclusion

We only need to include this header once. Drop the duplicate.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/mmc/sdhci.c b/drivers/mmc/sdhci.c
index f4eb655..ff871f8 100644
--- a/drivers/mmc/sdhci.c
+++ b/drivers/mmc/sdhci.c
@@ -15,7 +15,6 @@
 #include <malloc.h>
 #include <mmc.h>
 #include <sdhci.h>
-#include <dm.h>
 #include <asm/cache.h>
 #include <linux/bitops.h>
 #include <linux/delay.h>