efinix: program reports success (returns 0) when programming fails

[AndrewD]

Efinix: programming errors still result in a success return code so there is no way for a script to detect errors from the return value.

This interface needs to be able to propagate errors (not return void):

openFPGALoader/src/efinix.hpp

Line 30 in a395246

void program(unsigned int offset, bool unprotect_flash) override;

[trabucayre]

In fact for all vendor's drivers program method throw exceptions when something is wrong.
But it's true, changing program to a non void method may be more easy to manage
And for efinix most of errors doesn't produces exception.

[AndrewD]

If throwing an exception is the existing pattern then following this for Efinix would be sufficient for now - openfpgaloader just returning a non-zero value on error is all we need.

[trabucayre]

with this commit all errors are correctly handled by program() method.
It's good to you?