firewire: core/ohci: minor refactoring for computation of configuration ROM size

The size of space for configuration ROM is defined by IEEE 1212. The start
and end offsets are available as some macros in UAPI header.

This commit uses these macros to compute the size.

Link: https://lore.kernel.org/r/20240814131222.69949-4-o-takashi@sakamocchi.jp
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>

drivers/firewire/ohci.c

@@ -174,7 +174,7 @@ struct iso_context {
 	u8 tags;
 };
 
-#define CONFIG_ROM_SIZE 1024
+#define CONFIG_ROM_SIZE		(CSR_CONFIG_ROM_END - CSR_CONFIG_ROM)
 
 struct fw_ohci {
 	struct fw_card card;