mmc: replace BUG_ON with WARN_ON

Replace all cases of BUG_ON with WARN_ON where there is a chance
(with varying degrees of slim) that the kernel can continue without
incidence.

Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>
diff --git a/drivers/mmc/core/sdio.c b/drivers/mmc/core/sdio.c
index 58cf36e..2f3fb99 100644
--- a/drivers/mmc/core/sdio.c
+++ b/drivers/mmc/core/sdio.c
@@ -230,7 +230,7 @@
 	struct mmc_card *card;
 
 	BUG_ON(!host);
-	BUG_ON(!host->claimed);
+	WARN_ON(!host->claimed);
 
 	mmc_attach_bus(host, &mmc_sdio_ops);