mmc: atmel-mci: fix return value check of mmc_add_host()

mmc_add_host() may return error, if we ignore its return value,
it will lead two issues:
1. The memory that allocated in mmc_alloc_host() is leaked.
2. In the remove() path, mmc_remove_host() will be called to
   delete device, but it's not added yet, it will lead a kernel
   crash because of null-ptr-deref in device_del().

So fix this by checking the return value and calling mmc_free_host()
in the error path.

Fixes: 7d2be074 ("atmel-mci: Driver for Atmel on-chip MMC controllers")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Link: https://lore.kernel.org/r/20221108122819.429975-1-yangyingliang@huawei.comSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/atmel-mci.c

@@ -2222,6 +2222,7 @@ static int atmci_init_slot(struct atmel_mci *host,
 {
 	struct mmc_host			*mmc;
 	struct atmel_mci_slot		*slot;
+	int ret;
 
 	mmc = mmc_alloc_host(sizeof(struct atmel_mci_slot), &host->pdev->dev);
 	if (!mmc)
@@ -2305,11 +2306,13 @@ static int atmci_init_slot(struct atmel_mci *host,
 
 	host->slot[id] = slot;
 	mmc_regulator_get_supply(mmc);
-	mmc_add_host(mmc);
+	ret = mmc_add_host(mmc);
+	if (ret) {
+		mmc_free_host(mmc);
+		return ret;
+	}
 
 	if (gpio_is_valid(slot->detect_pin)) {
-		int ret;
-
 		timer_setup(&slot->detect_timer, atmci_detect_change, 0);
 
 		ret = request_irq(gpio_to_irq(slot->detect_pin),