[media] ddbridge: Replace vmalloc with vzalloc

vzalloc combines vmalloc and memset 0.

The Coccinelle semantic patch used to make this change is as follows:
@@
type T;
T *d;
expression e;
statement S;
@@

        d =
-            vmalloc
+            vzalloc
             (...);
        if (!d) S
-       memset(d, 0, sizeof(T));

Signed-off-by: Amitoj Kaur Chawla <amitoj1606@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>