cifs: consolidate error handling in several functions

cifs has a lot of complicated functions that have to clean up things on
error, but some of them don't have all of the cleanup code
well-consolidated. Clean up and consolidate error handling in several
functions.

This is in preparation of later patches that will need to put references
to the tcon link container.

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