kbuild: deb-pkg: make debian source package working again

Since commit c5bf2efb ("kbuild: deb-pkg: fix binary-arch and clean
in debian/rules"), the source package generated by 'make deb-pkg' fails
to build.

I terribly missed the fact that the intdeb-pkg target may regenerate
include/config/kernel.release due to the following in the top Makefile:

  %pkg: include/config/kernel.release FORCE

Restore KERNELRELEASE= option to avoid the kernel.release disagreement
between build-arch and binary-arch.

Fixes: c5bf2efb ("kbuild: deb-pkg: fix binary-arch and clean in debian/rules")
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

scripts/package/mkdebian

@@ -239,6 +239,7 @@ cat <<EOF > debian/rules
 #!$(command -v $MAKE) -f
 
 srctree ?= .
+KERNELRELEASE = ${KERNELRELEASE}
 
 build-indep:
 build-arch:
@@ -250,7 +251,9 @@ build: build-arch
 
 binary-indep:
 binary-arch: build-arch
-	\$(MAKE) -f \$(srctree)/Makefile ARCH=${ARCH} intdeb-pkg
+	\$(MAKE) -f \$(srctree)/Makefile ARCH=${ARCH} \
+	KERNELRELEASE=\$(KERNELRELEASE) intdeb-pkg
+
 clean:
 	rm -rf debian/files debian/linux-*
 	\$(MAKE) -f \$(srctree)/Makefile ARCH=${ARCH} clean