ARM: 7154/1: mach-bcmring: fix build error in dma.c

Fixes this build error:

 CC      arch/arm/mach-bcmring/dma.o
arch/arm/mach-bcmring/dma.c: In function 'dma_request_channel_dbg':
arch/arm/mach-bcmring/dma.c:1022: error: 'TASK_INTERRUPTIBLE' undeclared (first use in this function)
arch/arm/mach-bcmring/dma.c:1022: error: (Each undeclared identifier is reported only once
arch/arm/mach-bcmring/dma.c:1022: error: for each function it appears in.)
arch/arm/mach-bcmring/dma.c:1024: error: implicit declaration of function 'schedule'
arch/arm/mach-bcmring/dma.c:1027: error: implicit declaration of function 'signal_pending'
arch/arm/mach-bcmring/dma.c: In function 'dma_free_channel':
arch/arm/mach-bcmring/dma.c:1092: error: 'TASK_INTERRUPTIBLE' undeclared (first use in this function)
arch/arm/mach-bcmring/dma.c: In function 'dma_map_add_region':
arch/arm/mach-bcmring/dma.c:1946: error: dereferencing pointer to incomplete type
arch/arm/mach-bcmring/dma.c:1948: error: dereferencing pointer to incomplete type
arch/arm/mach-bcmring/dma.c:1955: error: dereferencing pointer to incomplete type
make[1]: *** [arch/arm/mach-bcmring/dma.o] Error 1
make: *** [arch/arm/mach-bcmring] Error 2

Signed-off-by: Maxin B. John <maxin.john@gmail.com>
Reviewed-by: Jiandong Zheng <jdzheng@broadcom.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mach-bcmring/dma.c

@@ -36,6 +36,7 @@
 #include <linux/mm.h>
 #include <linux/pfn.h>
 #include <linux/atomic.h>
+#include <linux/sched.h>
 #include <mach/dma.h>
 
 /* I don't quite understand why dc4 fails when this is set to 1 and DMA is enabled */