[SSSD] [PATCH] Fix list comparison in memberof module

[Simo Sorce]

When we replace the member attribute on an entry we calculate the list
of total addition vs deletions and then make sure a dn does not appear
in both at the same time.

The code was wrong and was skipping the next comparison each time a
match was found due to an array counter error.

This was causing unnecessary work to add entries that were already
present.

Simo.