package/read-edid: Fix compiler check, c++ is not needed

Fixes
http://autobuild.buildroot.net/results/8c1/8c11e463b68121fe0331acf9f8a42a1d3fef40c7//


and others

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>