partitions: Fix path based Find_Next_Storage

If a path is specified for Find_Next_Storage() and datamedia is
excluded, the function currently runs to the end of available
partitions and reports no other storage is available. Fix this by
restoring the original mount_point == search_path check to break the
loop. The subsequent partitions loop will skip data-media storage as
needed.

Change-Id: I92baed866cd36f13d851bd58ba5346e47edb142e