qt5base: fix VNC platform plugin build on big-endian machines

Fixes [1], [2]:

  In file included from qvncintegration.cpp:38:0:
  qvncscreen.h:76:22: error: expected ';' at end of member declaration
       bool swapBytes() const

[1] http://autobuild.buildroot.net/results/718/7180ad7d7e78f1c3ce6a1f83a5a8fcc5e0ac03a2
[2] http://autobuild.buildroot.net/results/14f/14f8c436b184192681fb79c7f0c0d0daa35f867b



Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>