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/Android.mk b/Android.mk
index ed92484..b16d937 100644
--- a/Android.mk
+++ b/Android.mk
@@ -113,6 +113,7 @@
 ifeq ($(KBUILD_OPTIONS),)
 KBUILD_OPTIONS += WLAN_PROPRIETARY=$(WLAN_PROPRIETARY)
 KBUILD_OPTIONS += TARGET_SUPPORTS_WEARABLES=$(TARGET_SUPPORTS_WEARABLES)
+KBUILD_OPTIONS += BOARD_OPENSOURCE_DIR=$(BOARD_OPENSOURCE_DIR)
 KBUILD_OPTIONS += KERNEL_TO_BUILD_ROOT_OFFSET=$(KERNEL_TO_BUILD_ROOT_OFFSET)
 endif