dtc: Fix summary calculation in testsuite

[Jon Loeliger]

So, like, the other day David Gibson mumbled:
> The bookkeeping for producing the testsuite summary (total number of
> tests passed, failed and so forth) is broken.  It uses $? across
> several tests, but for checks after the first, the value of $? will no
> longer contain the original return code, but just that from the
> previous test.  This patch fixes the problem.
> 
> Signed-off-by: David Gibson <david at gibson.dropbear.id.au>

Applied.

Thanks,
jdl