connector: Fix incompatible pointer type warning

Commit 7069331 (connector: Provide the sender's credentials to the
callback, 2009-10-02) changed callbacks to take two arguments but missed
this one.

drivers/connector/cn_proc.c: In function ‘cn_proc_init’:
drivers/connector/cn_proc.c:263: warning: passing argument 3 of
‘cn_add_callback’ from incompatible pointer type

Signed-off-by: Stephen Boyd <bebarino@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>