mmc: core: remove redundant card null check to mmc_can_sleep()

Note that only _mmc_suspend() will call mmc_can_sleep(). And card is
checked before in mmc_can_poweroff_notify().
Signed-off-by: Yue Hu <huyue2@yulong.com>
Link: https://lore.kernel.org/r/20210115034506.646-1-zbestahu@gmail.comSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/core/mmc.c

@@ -1895,7 +1895,7 @@ static int mmc_init_card(struct mmc_host *host, u32 ocr,
 
 static int mmc_can_sleep(struct mmc_card *card)
 {
-	return (card && card->ext_csd.rev >= 3);
+	return card->ext_csd.rev >= 3;
 }
 
 static int mmc_sleep(struct mmc_host *host)