cifs: turn BCC into a static inlined function

It's a bad idea to have macro functions that reference variables more
than once, as the arguments could have side effects. Turn BCC() into
a static inlined function instead.

While we're at it, make it return a void * to discourage anyone from
dereferencing it as-is.

Reported-and-acked-by: David Howells <dhowells@redhat.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>
Signed-off-by: Pavel Shilovsky <piastry@etersoft.ru>
Signed-off-by: Steve French <sfrench@us.ibm.com>