mmc: sunplus: fix return value check of mmc_add_host()

In the Linux kernel, the following vulnerability has been resolved: mmc: sunplus: fix return value check of mmc_add_host() mmc_add_host() may return error, if we ignore its return value, 1. the memory allocated in mmc_alloc_host() will be leaked 2. null-ptr-deref will happen when calling mmc_remove_host() in remove function spmmc_drv_remove() because deleting not added device. Fix this by checking the return value of mmc_add_host(). Moreover, I fixed the error handling path of spmmc_drv_probe() to clean up.