D10415: Fix realDpi function for Mac

[Sergio Bragin]

sbragin added a comment.


  I have tested against Qt 5.9.3 and 5.10 on Mac OS 10.12.

REPOSITORY
  R223 Okular

REVISION DETAIL
  https://phabricator.kde.org/D10415

To: sbragin, #okular
Cc: ltoscano, #okular, michaelweghorn, ngraham, aacid