shareddata.h: Fix a new GCC 9 warning (Wdeprecated-copy)

In file included from /devel/v4l/kaffeine/src/dvb/dvbchanneldialog.h:26,

from /devel/v4l/kaffeine/src/dvb/dvbscandialog.cpp:37:

/devel/v4l/kaffeine/src/dvb/dvbchannel.h: In copy constructor ‘DvbChannel::DvbChannel(const DvbChannel&)’:
/devel/v4l/kaffeine/src/dvb/dvbchannel.h:30:7: warning: implicitly-declared ‘SharedData::SharedData(const SharedData&)’ is deprecated [-Wdeprecated-copy]

30 | class DvbChannel : public SharedData, public SqlKey
   |       ^~~~~~~~~~

In file included from /devel/v4l/kaffeine/src/dvb/dvbchannel.h:26,

from /devel/v4l/kaffeine/src/dvb/dvbchanneldialog.h:26,
from /devel/v4l/kaffeine/src/dvb/dvbscandialog.cpp:37:

/devel/v4l/kaffeine/src/dvb/../shareddata.h:32:14: note: because ‘SharedData’ has user-provided ‘SharedData& SharedData::operator=(const SharedData&)’

32 |  SharedData &operator=(const SharedData &)
   |              ^~~~~~~~

/devel/v4l/kaffeine/src/dvb/dvbscandialog.cpp: In member function ‘void DvbScanDialog::addSelectedChannels()’:
/devel/v4l/kaffeine/src/dvb/dvbscandialog.cpp:554:34: note: synthesized method ‘DvbChannel::DvbChannel(const DvbChannel&)’ first required here

554 |    DvbChannel newChannel(*channel);
    |                                  ^

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>