cifs: clean up ordering in exit_cifs

...ensure that we undo things in the reverse order from the way they
were done. In truth, the ordering doesn't matter for a lot of these,
but it's still better to do it that way to be sure.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>