Builds in the v2019 OBS were failing in the gencontrol target since the build
suffix used there is `v2019.0b1` and the regest was not matching the `.` dot.

This was not an issue in the `v2020dev0` project since its build suffix does
not contain dots:

    $ VERSION=4.19.37-5co1bv2020dev0b1; echo "$VERSION" | sed -rne 's,[^b]*b([a-z0-9]+)$$,\1,p'
    v2020dev0b1
    $ VERSION=4.19.37-5co1bv2019.0b1; echo "$VERSION" | sed -rne 's,[^b]*b([a-z0-9]+)$$,\1,p'
    4.19.37-5co1b1 # ARGH
    $ VERSION=4.19.37-5co1bv2019.0b1; echo "$VERSION" | sed -rne 's,[^b]*b([a-z0-9.]+)$$,\1,p'
    v2019.0b1
    $ VERSION=4.19.37-5co1bv2020dev0b1; echo "$VERSION" | sed -rne 's,[^b]*b([a-z0-9.]+)$$,\1,p'
    v2020dev0b1

Signed-off-by: Emanuele Aina <emanuele.aina@collabora.com>