cx88-video build fix

alpha:

drivers/media/video/cx88/cx88-video.c: In function 'cx8800_initdev':
drivers/media/video/cx88/cx88-video.c:1782: error: 'DMA_32BIT_MASK' undeclared (first use in this function)
drivers/media/video/cx88/cx88-video.c:1782: error: (Each undeclared identifier is reported only once
drivers/media/video/cx88/cx88-video.c:1782: error: for each function it appears in.)

Cc: Mauro Carvalho Chehab <mchehab@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/media/video/cx88/cx88-alsa.c b/drivers/media/video/cx88/cx88-alsa.c
index 3956c25..2d666b5 100644
--- a/drivers/media/video/cx88/cx88-alsa.c
+++ b/drivers/media/video/cx88/cx88-alsa.c
@@ -27,6 +27,8 @@
 #include <linux/init.h>
 #include <linux/device.h>
 #include <linux/interrupt.h>
+#include <linux/dma-mapping.h>
+
 #include <asm/delay.h>
 #include <sound/driver.h>
 #include <sound/core.h>