CVE-2022-50268 mmc: moxart: fix return value check of mmc_add_host()

In the Linux kernel, the following vulnerability has been resolved: mmc: moxart: fix return value check of mmcaddhost mmcaddhost may return error, if we ignore its return value, the memory that allocated in mmcallochost will be leaked and it will lead a kernel crash because of deleting not added...