pulseaudio: fix missing staging library directory /usr/lib/pulseaudio/

This library directory is required to link
against pulseaudio. e.g. mpd with pulseaudio support.

Signed-off-by: Alexander Couzens <lynxis@base45.de>

git-svn-id: svn://svn.openwrt.org/openwrt@36103 3c298f89-4303-0410-b956-a3cf2f4a3e73