hal: fix a typo in make file

Fix a typo in Android.mk that was preventing
enablement of dynamic ECNS feature.

Change-Id: I31413e87de9c871154f7e54792a45933a10d1ef6
diff --git a/hal/Android.mk b/hal/Android.mk
index fec5236..22ac59f 100644
--- a/hal/Android.mk
+++ b/hal/Android.mk
@@ -393,7 +393,7 @@
     LOCAL_SHARED_LIBRARIES += libaudio_log_utils
 endif
 
-ifeq ($(strip $($AUDIO_FEATURE_ENABLED_DYNAMIC_ECNS)),true)
+ifeq ($(strip $(AUDIO_FEATURE_ENABLED_DYNAMIC_ECNS)),true)
     LOCAL_CFLAGS += -DDYNAMIC_ECNS_ENABLED
 endif