buildman: Correct CROSS_COMPILE output for sandbox

At present, 'buildman -A sandbox' adds the path containing the
toolchain at present. We can assume that this is in the path and
we don't want to set CROSS_COMPILE=/bin/ so change this to align
with what MakeEnvironment() does.

Signed-off-by: Simon Glass <sjg@chromium.org>
1 file changed