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>
diff --git a/drivers/mmc/card/mmc_test.c b/drivers/mmc/card/mmc_test.c
index 2529601..a067fe4 100644
--- a/drivers/mmc/card/mmc_test.c
+++ b/drivers/mmc/card/mmc_test.c
@@ -1256,6 +1256,8 @@
 	if (ret)
 		return ret;
 
+	dev_info(&card->dev, "Card claimed for testing.\n");
+
 	return 0;
 }