mmc: core: fix return value check in devm_mmc_alloc_host()

mmc_alloc_host() returns NULL pointer not PTR_ERR(), if it
fails, so replace the IS_ERR() check with NULL pointer check.

In commit 418f7c2d ("mmc: meson-gx: use devm_mmc_alloc_host"),
it checks NULL pointer not PTR_ERR, if devm_mmc_alloc_host() fails,
so make it to return NULL pointer to keep same with mmc_alloc_host(),
the drivers don't need to change the error handle when switch to
use devm_mmc_alloc_host().

Fixes: 80df83c2 ("mmc: core: add devm_mmc_alloc_host")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: Heiner Kallweit <hkallweit1@gmail.com>
Link: https://lore.kernel.org/r/20230217024333.4018279-1-yangyingliang@huawei.comSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/core/host.c

@@ -599,12 +599,12 @@ struct mmc_host *devm_mmc_alloc_host(struct device *dev, int extra)
 
 	dr = devres_alloc(devm_mmc_host_release, sizeof(*dr), GFP_KERNEL);
 	if (!dr)
-		return ERR_PTR(-ENOMEM);
+		return NULL;
 
 	host = mmc_alloc_host(extra, dev);
-	if (IS_ERR(host)) {
+	if (!host) {
 		devres_free(dr);
-		return host;
+		return NULL;
 	}
 
 	*dr = host;