xen/serial: scif: Rework how the parameters are found

clang 11 will throw the following error while build Xen:

scif-uart.c:333:33: error: cast to smaller integer type 'enum port_types' from 'const void *' [-Werror,-Wvoid-pointer-to-enum-cast]
    uart->params = &port_params[(enum port_types)match->data];
                                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~

The error can be prevented by directly storing a pointer to the port
parameters rather than the a cast of the port type.

Signed-off-by: Julien Grall <jgrall@amazon.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

xen/drivers/char/scif-uart.c

@@ -286,8 +286,8 @@ static struct uart_driver __read_mostly scif_uart_driver = {
 
 static const struct dt_device_match scif_uart_dt_match[] __initconst =
 {
-    { .compatible = "renesas,scif",  .data = (void *)SCIF_PORT },
-    { .compatible = "renesas,scifa", .data = (void *)SCIFA_PORT },
+    { .compatible = "renesas,scif",  .data = &port_params[SCIF_PORT] },
+    { .compatible = "renesas,scifa", .data = &port_params[SCIFA_PORT] },
     { /* sentinel */ },
 };
 
@@ -330,7 +330,7 @@ static int __init scif_uart_init(struct dt_device_node *dev,
 
     match = dt_match_node(scif_uart_dt_match, dev);
     ASSERT( match );
-    uart->params = &port_params[(enum port_types)match->data];
+    uart->params = match->data;
 
     uart->vuart.base_addr  = addr;
     uart->vuart.size       = size;