kbuild: deb-pkg: allow to run debian/rules from output directory

'make O=... deb-pkg' creates the debian directory in the output
directory. However, currently it is impossible to run debian/rules
created in the separate output directory.

This commit delays the $(srctree) expansion by escaping '$' and by
quoting the entire command, making it possible to run debian/rules in
the output directory.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <n.schier@avm.de>

scripts/package/debian/rules

@@ -19,7 +19,7 @@ binary: binary-arch binary-indep
 binary-indep: build-indep
 binary-arch: build-arch
 	$(MAKE) -f $(srctree)/Makefile $(make-opts) \
-	run-command KBUILD_RUN_COMMAND=+$(srctree)/scripts/package/builddeb
+	run-command KBUILD_RUN_COMMAND='+$$(srctree)/scripts/package/builddeb'
 
 .PHONY: build build-indep build-arch
 build: build-arch build-indep