totemconfig: Fix compiler warning

Compiler is unable to understand relation between members and
num_configured and warns about uninitialized members. Instead of
initializing members to 0 and (potentially after some code
refactor) let code fall to display error message, more explicit method
of assert is used.

Signed-off-by: Jan Friesse <jfriesse@redhat.com>
Reviewed-by: Christine Caulfield <ccaulfie@redhat.com>