Add const overload for QLoggingCategory::operator()()

Change 85e57653 caused a compile error for code that does

  Q_DECLARE_LOGGING_CATEGORY(cat);
  //..
  qCDebug(cat()) << // ...

error: C3848: expression having type 'const QLoggingCategory' would lose
some const-volatile qualifiers in order to call 'QLoggingCategory
&QLoggingCategory::operator ()(void)'

This is a regression from Qt 5.2. Fix the error by adding a const version
of operator()().

Change-Id: I2fb04f2e155962adee0f98089fc5a159000bef56
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

0 files changed, 0 insertions, 0 deletions