Most of the functions that are called in the probe callback are
devm managed, or all but mipi_dsi_host_register(): simplify the probe
function's error paths with dev_err_probe() and remove the lonely
instance of `goto err_unregister_host` by just directly calling the
mipi_dsi_host_unregister() function in the devm_request_irq() error
path, allowing to also remove the same label.