cifs: Pass GLOBAL_ROOT_UID and GLOBAL_ROOT_GID to keyring_alloc

keyring_alloc has been updated to take a kuid_t and kgid_t so
pass GLOBAL_ROOT_UID instead of 0 for the uid and GLOBAL_ROOT_GID
instead of 0 for the gid.

Cc: Steve French <smfrench@gmail.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>