wlan: Update wlan source directory path for sdm429w

Use BOARD_OPENSOURCE_DIR to get wlan source directory path
for sdm429w target.

Change-Id: I24a41941ceb2a384040313a6f58a90d625ace245
CRs-Fixed: 2846100
diff --git a/Kbuild b/Kbuild
index 7414ebd..e186b91 100644
--- a/Kbuild
+++ b/Kbuild
@@ -110,7 +110,7 @@
 else
 ifneq ($(ANDROID_BUILD_TOP),)
 ifeq ($(TARGET_PRODUCT),sdm429w)
-    WLAN_BLD_DIR := $(ANDROID_BUILD_TOP)/device/qcom/sdm429w/common/opensource/wlan
+    WLAN_BLD_DIR := $(ANDROID_BUILD_TOP)/$(BOARD_OPENSOURCE_DIR)/wlan
 else
     WLAN_BLD_DIR := $(ANDROID_BUILD_TOP)/vendor/qcom/opensource/wlan
 endif #TARGET_PRODUCT