freerdp: alsa support needs mixer as well

Fixes:
http://autobuild.buildroot.net/results/5ed/5edaa6654b90299ead5255d1cbdf79eb8b40fc6f/

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/freerdp/freerdp.mk

@@ -26,7 +26,7 @@ else
 FREERDP_CONF_OPTS += -DWITH_FFMPEG=OFF
 endif
 
-ifeq ($(BR2_PACKAGE_ALSA_LIB),y)
+ifeq ($(BR2_PACKAGE_ALSA_LIB_MIXER),y)
 FREERDP_CONF_OPTS += -DWITH_ALSA=ON
 FREERDP_DEPENDENCIES += alsa-lib
 else