V4L/DVB (12731): cx25821: Add missing include

/home/v4l/master/v4l/cx25821-audups11.c:99: error: implicit declaration of function 'lock_kernel'
/home/v4l/master/v4l/cx25821-audups11.c:112: error: implicit declaration of function 'unlock_kernel'
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>

drivers/staging/cx25821/cx25821.h

@@ -32,6 +32,7 @@
 #include <linux/delay.h>
 #include <linux/sched.h>
 #include <linux/kdev_t.h>
+#include <linux/smp_lock.h>
 
 #include <media/v4l2-common.h>
 #include <media/v4l2-device.h>