ARM: CSR: fix build error due to new mdesc->dma_zone_size

commit 98b0124f
"ARM: mach-prima2: move ARM_DMA_ZONE_SIZE to mdesc->dma_zone_size"
causes building error:
arch/arm/mach-prima2/prima2.c:39:19: error: 'SZ_256M' undeclared here
(not in a function)
Signed-off-by: Barry Song <baohua.song@csr.com>

arch/arm/mach-prima2/prima2.c

@@ -8,6 +8,7 @@
 
 #include <linux/init.h>
 #include <linux/kernel.h>
+#include <asm/sizes.h>
 #include <asm/mach-types.h>
 #include <asm/mach/arch.h>
 #include <linux/of.h>