gobex: Fix a compilation error for the compatibility with LLVM

gobex: Fix a compilation error for the compatibility with LLVM

The C Standard, subclause 7.16.1.4, paragraph 4 [ISO/IEC 9899:2011], states:
The parameter parmN is the identifier of the rightmost parameter in
the variable parameter list in the function definition (the one just
before the ...). If the parameter parmN is declared with the register
storage class, with a function or array type, or with a type that is
not compatible with the type that results after application of the
default argument promotions, the behavior is undefined.