qcacld-3.0: correct the path for qca-wifi-host-cmn in Kbuild

From qcacld30-hl_git.bb/qcacld30-ll_git.bb, qca-wifi-host-cmn
is in the same directory with qcacld-3.0(<src_root>/wlan/),
so correct the path for it in Kbuild.

Change-Id: I5c552d2f89cd7b6832c37d6785cfc5a0d00c795d
CRs-Fixed: 2005755

Kbuild

@@ -235,7 +235,7 @@ endif
 endif
 
 # If not set, assume, Common driver is with in the build tree
-WLAN_COMMON_ROOT ?= qca-wifi-host-cmn
+WLAN_COMMON_ROOT ?= ../qca-wifi-host-cmn
 WLAN_COMMON_INC ?= $(WLAN_ROOT)/$(WLAN_COMMON_ROOT)
 
 ifneq ($(CONFIG_MOBILE_ROUTER), y)