tools: shut up a gcc 7.1 warning

/home/mchehab/devel/kaffeine/tools/convertscanfiles.cpp:425:8: warning: this statement may fall through [-Wimplicit-fallthrough=]

type = DvbTransponderBase::DvbS2;
~~~~~^~~~~~~~~~~~~~~~~~~~

/home/mchehab/devel/kaffeine/tools/convertscanfiles.cpp:428:2: note: here

case DvbTransponderBase::DvbS2: {
^~~~

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>