uboot-phytec

patman: Fix doctest StringIO import for python 3.x

In python 3.x StringIO is no longer a module, and the class can instead
be found in the io module. Adjust the code in the doctest input to
account for both.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Acked-by: Simon Glass <sjg@chromium.org>