mmc: check the return value of mmc_select_mode_and_width()

Since commit 01298da3 ("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: 01298da3 ("mmc: Change mode when switching to a boot partition")
Signed-off-by: NMasahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: NJaehoon Chung <jh80.chung@samsung.com>

drivers/mmc/mmc.c

@@ -2577,7 +2577,7 @@ static int mmc_startup(struct mmc *mmc)
 		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)