[dovecot/core] 47758f: m4: Fix sodium checks

[GitHub]

  Branch: refs/heads/master
  Home:   https://github.com/dovecot/core
  Commit: 47758f9335a08d249461f35813f65e4ca24d4e73
      https://github.com/dovecot/core/commit/47758f9335a08d249461f35813f65e4ca24d4e73
  Author: Aki Tuomi <aki.tuomi at dovecot.fi>
  Date:   2017-12-13 (Wed, 13 Dec 2017)

  Changed paths:
    M m4/want_sodium.m4

  Log Message:
  -----------
  m4: Fix sodium checks

Make sure it actually has password checking function