schifra: fix build of examples and add hash

The OPTIONS argument passed to make had a redundant -o option, leading
to:

g++ -pipe -Os   -o -o schifra_reed_solomon_speed_evaluation schifra_reed_solomon_speed_evaluation.cpp -lstdc++ -lm
arm-linux-musleabi-g++: error: schifra_reed_solomon_speed_evaluation: No such file or directory

Fixes:
http://autobuild.buildroot.net/results/2143b4f6f22f50ccb4af36732cc7d9304daa3ff9/



This error didn't occur before because upstream has silently updated
the tarball. To protect against this in the future, a hash is added as
well.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>