[U-Boot] Please fix warnings in NIOS2 boards

Hi.

When I build NIOS2 boards, warnings are displayed.

common/cmd_test.c: In function `do_test': common/cmd_test.c:66: warning: 'op' might be used uninitialized in this function common/cmd_test.c:66: warning: 'adv' might be used uninitialized in this function

Could anybody fix them?

Best Regards Masahiro Yamada