sbus_codegen_tests: Suppress warning Wmaybe-uninitialized
    
    There is a warning with gcc 4.8
    
    src/tests/sbus_codegen_tests.c:1131:18: warning: 'exp_values' may be used
        uninitialized in this function [-Wmaybe-uninitialized]
         const char **exp_values;
                      ^
    Reviewed-by: Pavel Březina <pbrezina@redhat.com>
    
    (cherry picked from commit 617d5161d4ec454afc673ce1836b02f82435b347)