mmc: via-sdmmc: fix return value check of mmc_add_host()

mmc: via-sdmmc: 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().

Fix this by checking the return value and goto error path which
will call mmc_free_host().

Fixes: f0bf7f61b840 ("mmc: Add new via-sdmmc host controller driver")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Link: https://lore.kernel.org/r/20221108130949.1067699-1-yangyingliang@huawei.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>