osc: use upstream branch name instead of HEAD for about dialog version

Since the adi_update_tools script does git checkouts into unnamed
branches the previous method of retrieving the branch name only returns
'HEAD' and not the upstream branch name that we want.

Signed-off-by: Tim Harder <timothy.harder@analog.com>
osc: fix makefile syntax issue

Signed-off-by: Tim Harder <timothy.harder@analog.com>