mmc_test: print message when attaching to card

Make it a bit more obvious that the card has been claimed by the
mmc_test driver so that people don't have to wonder why their block
device never shows up.
Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>

drivers/mmc/card/mmc_test.c

@@ -1256,6 +1256,8 @@ static int mmc_test_probe(struct mmc_card *card)
 	if (ret)
 		return ret;
 
+	dev_info(&card->dev, "Card claimed for testing.\n");
+
 	return 0;
 }