staging: comedi: Remove useless cast.

Variable dac_data is already declared as of type u8. Again explicit type
casting of dac_data to u8, is not required. Hence this patch removes it
by using the following coccinelle script.

@@
type T;
T *ptr;
T p;
@@
(
- (T *)(&p)
+ &p
|
- (T *)ptr
+ ptr
|
- (T *)(ptr)
+ ptr
|
- (T)(p)
+ p
)

Signed-off-by: Varsha Rao <rvarsha016@gmail.com>
Acked-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>