kbuild: deb-pkg: don't set KBUILD_BUILD_VERSION unconditionally

kbuild: deb-pkg: don't set KBUILD_BUILD_VERSION unconditionally

In ThinPro, we use the convention <upstream_ver>+hp<patchlevel> for
the kernel package. This does not have a dash in the name or version.
This is built by editing ".version" before a build, and setting
EXTRAVERSION="+hp" and KDEB_PKGVERSION make variables:

    echo 68 > .version
    make -j<n> EXTRAVERSION="+hp" bindeb-pkg KDEB_PKGVERSION=6.12.2+hp69

    .deb name: linux-image-6.12.2+hp_6.12.2+hp69_amd64.deb

Since commit 7d4f07d5cb71 ("kbuild: deb-pkg: squash
scripts/package/deb-build-option to debian/rules"), this no longer
works. The deb build logic changed, even though, the commit message
implies that the logic should be unmodified.

Before, KBUILD_BUILD_VERSION was not set if the KDEB_PKGVERSION did
not contain a dash. After the change KBUILD_BUILD_VERSION is always
set to KDEB_PKGVERSION. Since this determines UTS_VERSION, the uname
output to look off:

    (now)      uname -a: version 6.12.2+hp ... #6.12.2+hp69
    (expected) uname -a: version 6.12.2+hp ... #69

Update the debian/rules logic to restore the original behavior.

Fixes: 7d4f07d5cb71 ("kbuild: deb-pkg: squash scripts/package/deb-build-option to debian/rules")
Signed-off-by: Alexandru Gagniuc <alexandru.gagniuc@hp.com>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>