busybox

testsuite: check CONFIG_DESKTOP before using 'od -t'

The '-t' option for od is enabled by CONFIG_DESKTOP. So
check this config before using 'od -t' in test cases.

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>