soc/intel: rename uart_max_index

The name `..._index` is confusing since the maximum index of an array is
not `ARRAY_SIZE(array)` but `ARRAY_SIZE(array) - 1`.

Rename `uart_max_index` to `uart_ctrlr_config_size` to make the name
match the variable´s value.

Change-Id: I7409c9dc040c3c6ad718abc96f268c187d50d79c
Signed-off-by: Michael Niewöhner <foss@mniewoehner.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/49305
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Furquan Shaikh <furquan@google.com>

src/soc/intel/alderlake/uart.c

@@ -44,4 +44,4 @@ const struct uart_controller_config uart_ctrlr_config[] = {
 	}
 };
 
-const int uart_max_index = ARRAY_SIZE(uart_ctrlr_config);
+const int uart_ctrlr_config_size = ARRAY_SIZE(uart_ctrlr_config);