ARM: EXYNOS: Add missing definition for IRQ_I2S0

This fixes following build error when sound support is selected
on EXYNOS4 platform.

sound/soc/samsung/idma.c: In function ‘idma_close’:
sound/soc/samsung/idma.c:327:11: error: ‘IRQ_I2S0’ undeclared (first use in this function)
Signed-off-by: NTushar Behera <tushar.behera@linaro.org>
Signed-off-by: NKukjin Kim <kgene.kim@samsung.com>

arch/arm/mach-exynos/include/mach/irqs.h

@@ -212,6 +212,8 @@
 #define IRQ_MFC				EXYNOS4_IRQ_MFC
 #define IRQ_SDO				EXYNOS4_IRQ_SDO
 
+#define IRQ_I2S0			EXYNOS4_IRQ_I2S0
+
 #define IRQ_ADC				EXYNOS4_IRQ_ADC0
 #define IRQ_TC				EXYNOS4_IRQ_PEN0