mmc: check the return value of mmc_select_mode_and_width()

Since commit 01298da31d92 ("mmc: Change mode when switching to a boot
partition"), errors in mmc_select_mode_and_width() are ignored.
The return value should be checked.

Fixes: 01298da31d92 ("mmc: Change mode when switching to a boot partition")
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>
diff --git a/drivers/mmc/mmc.c b/drivers/mmc/mmc.c
index 6a2b855..2eb5e9d 100644
--- a/drivers/mmc/mmc.c
+++ b/drivers/mmc/mmc.c
@@ -2577,7 +2577,7 @@
 		err = mmc_get_capabilities(mmc);
 		if (err)
 			return err;
-		mmc_select_mode_and_width(mmc, mmc->card_caps);
+		err = mmc_select_mode_and_width(mmc, mmc->card_caps);
 	}
 #endif
 	if (err)