qemu-kvm: fix pulseaudio detection in configure pulse/simple.h does not include stdlib.h We cannot use NULL since it may not be defined Use 0 instead Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com> Reviewed-by: Peter Maydell <peter.maydell@linaro.org> Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>