binfmt: Fix some compilation issues introduced in previous changes.  Verfied with the STM32F4-Discovery ELF configuration.

    binfmt:  schedule_unload() is an internal OS function and must not alter the errno variable.

    binfmt:  unload_module() is an internal OS function and must not alter the errno variable.

    binfmt:  load_module() is an internal OS function and must not alter the errno variable.

    binfmt:  exec_module() is an internal OS function and must not alter the errno variable.