build: fix minimal mixup in gitinfo suffix
the original version of this had issues with tagless repositories; to
fix that I removed the "-g" part from one of the regexes. I then failed
to add those 2 characters back, leading to version numbers like
"0.99.220123456" instead of "0.99.22-ga123456". Let's put the "-g"
back...
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>