cgroup: fix sock_cgroup_data initialization on earlier compilers

sock_cgroup_data is a struct containing an anonymous union.
sock_cgroup_set_prioidx() and sock_cgroup_set_classid() were
initializing a field inside the anonymous union as follows.

 struct sock_ccgroup_data skcd_buf = { .val = VAL };

While this is fine on more recent compilers, gcc-4.4.7 triggers the
following errors.

 include/linux/cgroup-defs.h: In function ‘sock_cgroup_set_prioidx’:
 include/linux/cgroup-defs.h:619: error: unknown field ‘val’ specified in initializer
 include/linux/cgroup-defs.h:619: warning: missing braces around initializer
 include/linux/cgroup-defs.h:619: warning: (near initialization for ‘skcd_buf.<anonymous>’)

This is because .val belongs to the anonymous union nested inside the
struct but the initializer is missing the nesting.  Fix it by adding
an extra pair of braces.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Alaa Hleihel <alaa@dev.mellanox.co.il>
Fixes: bd1060a1 ("sock, cgroup: add sock->sk_cgroup")
Signed-off-by: David S. Miller <davem@davemloft.net>