mmc: Print error code for mmc_complete_init failure

Print the error code for non-zero (failure case) instead
of making debug statement without any condition, this
usually gives proper clue in failure condition.

Log:

drivers/mmc/mmc.c

@@ -1751,7 +1751,9 @@ int mmc_init(struct mmc *mmc)
 
 	if (!err)
 		err = mmc_complete_init(mmc);
-	debug("%s: %d, time %lu\n", __func__, err, get_timer(start));
+	if (err)
+		printf("%s: %d, time %lu\n", __func__, err, get_timer(start));
+
 	return err;
 }