mmc: Ensure prototypes for SD API are visible in sd.c

So we know the implementation and prototypes agree with each other.
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Reviewed-by: Chris Ball <cjb@laptop.org>
Signed-off-by: Chris Ball <cjb@laptop.org>

drivers/mmc/core/sd.c

@@ -21,6 +21,7 @@
 #include "core.h"
 #include "bus.h"
 #include "mmc_ops.h"
+#include "sd.h"
 #include "sd_ops.h"
 
 static const unsigned int tran_exp[] = {