portaudio: disable parallel build

The portaudio build system contains a race condition, which gets triggered
by high BR2_JLEVEL settings - It tries to use libportaudio.la before it is
created:

make[3]: *** No rule to make target `../../../lib/libportaudio.la',
needed by `libportaudiocpp.la'.  Stop.

Fix it by disabling parallel build.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/multimedia/portaudio/portaudio.mk

@@ -8,6 +8,7 @@ PORTAUDIO_VERSION = V19
 PORTAUDIO_SITE = http://www.portaudio.com/archives
 PORTAUDIO_SOURCE = pa_stable_v19_20110326.tgz
 PORTAUDIO_INSTALL_STAGING = YES
+PORTAUDIO_MAKE = $(MAKE1)
 
 PORTAUDIO_DEPENDENCIES = \
        $(if $(BR2_PACKAGE_PORTAUDIO_WITH_ALSA),alsa-lib)