python-dns: use --prefix & --root config options

Does not fix anything, just brings it inline with the
other python packages.

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>

lang/python-dns/Makefile

@@ -36,7 +36,7 @@ endef
 
 define Build/Compile
 	$(call Build/Compile/PyMod,,\
-		install --prefix="$(PKG_INSTALL_DIR)/usr" \
+		install --prefix=/usr --root="$(PKG_INSTALL_DIR)" \
 	)
 endef