serial: sb1250-duart: clean up after SIBYTE_BCM1x55 removal

With commit b984d7b ("MIPS: sibyte: Remove unused config option
SIBYTE_BCM1x55"), an #if in the Broadcom SiByte DUART driver can be
simplified.

Simplify the prepreprocessor condition after config SIBYTE_BCM1x55 removal.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Link: https://lore.kernel.org/r/20230323071053.417-1-lukas.bulwahn@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/sb1250-duart.c

@@ -41,7 +41,7 @@
 #include <asm/sibyte/swarm.h>
 
 
-#if defined(CONFIG_SIBYTE_BCM1x55) || defined(CONFIG_SIBYTE_BCM1x80)
+#if defined(CONFIG_SIBYTE_BCM1x80)
 #include <asm/sibyte/bcm1480_regs.h>
 #include <asm/sibyte/bcm1480_int.h>