qt: fix missing target

Fix :
 http://autobuild.buildroot.net/results/093/09302c153418c3af6dc4cdd12a0149505cfbca0b/
 http://autobuild.buildroot.net/results/96f/96f8a9758f0116aec999028fde1b9c983c143809/



sh target must be provided instead of generic to have the correct QT_NO_FPU
behaviour.

Signed-off-by: Gwenhael Goavec-Merou <gwenhael.goavec-merou@trabucayre.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>