bootmenu: fix menu API error handling

U-Boot menu framework(common/menu.c) returns 1 if it is successful,
returns negative value if it fails.

Signed-off-by: Masahisa Kojima <masahisa.kojima@linaro.org>
Acked-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
1 file changed