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

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: 7d2be0749a59 ("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.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>