devtool: modify: Catch git submodule error for go code

One of the git submodule commands failed for source extracted for
recipes using go.bbclass.  The root cause is probably the path set up
by go_do_unpack which makes S and gitroot not match.

This patch does not fix the root problem, but at least it is no worse
than before the git submodule support.

The extracted source will still have two .git folders, one in S
created by devtool and one in the go path which will contain the tru
git history.

[ YOCTO #15483 ]

Signed-off-by: Anton Almqvist <antonal@axis.com>
Signed-off-by: Ola x Nilsson <olani@axis.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>