audio/lsp-plugins-lv2: fix build on powerpc*

Merges https://github.com/lsp-plugins/lsp-plugin-fw/commit/746181e62cf9525237a8e860d94ecbec6436694b.

ld: error: undefined symbol: lsp::ctl::Factory::pRoot

referenced by WidgetNode.cpp

/wrkdirs/usr/ports/audio/lsp-plugins-lv2/work/lsp-plugins/.build/host/lsp-plugin-fw/lsp-plugin-fw-ui.o:(.toc+0x78)