mmc: sdhci-pltfm: call platform_get_irq() before sdhci_alloc_host()
Swap the call order of sdhci_alloc_host() and platform_get_irq().
It makes sdhci_alloc_host() the last function that can fail in the
sdhci_pltfm_init(). So, we can drop the sdhci_free_host() call from
the failure path.