ARM: riscpc: use definition for serial port interrupt

Rather than using a plain integer, use the definition already provided.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/arch/arm/mach-rpc/riscpc.c b/arch/arm/mach-rpc/riscpc.c
index 30baaa8..b4db100 100644
--- a/arch/arm/mach-rpc/riscpc.c
+++ b/arch/arm/mach-rpc/riscpc.c
@@ -152,7 +152,7 @@
 static struct plat_serial8250_port serial_platform_data[] = {
 	{
 		.mapbase	= 0x03010fe0,
-		.irq		= 10,
+		.irq		= IRQ_SERIALPORT,
 		.uartclk	= 1843200,
 		.regshift	= 2,
 		.iotype		= UPIO_MEM,