docbook-utils-native: Unbreak the build after source and build dir split

docbook-utils-native: Unbreak the build after source and build dir split

docbook-utils-native started to install frontends and backends in
wrong locations after this change. The absolute build and source
directories were being created in install locations and the recipes
using docbook-utils-native were complaining like dbus-java is saying

| jw: There is no frontend called
"/b/kraj/jlinux-next/poky/build/tmp-eglibc/sysroots/x86_64-linux/usr/share/sgml/docbook/utils-0.6.14/frontends/docbook".
| make: *** [CreateInterface.1] Error 2
| ERROR: oe_runmake failed

Rightly so because now they are installed under
/b/kraj/jlinux-next/poky/build/tmp-eglibc/sysroots/x86_64-linux/usr/share/sgml/docbook/utils-0.6.14/b/kraj/jlinux-next/poky/build/tmp-eglibc/work/x86_64-linux/docbook-utils-native/0.6.14-r3/

This patch fixes the install to be like it was but consider
the build and sourcedir split.

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>