qcacld-3.0: Add qdf_str to Kbuild

Include the recently added qdf_str files to the Kbuild.

Change-Id: Id6753691e950ac06114de95d71068f45c48003a5
CRs-Fixed: 2184473
diff --git a/Kbuild b/Kbuild
index 8f68421..f44c9ac 100644
--- a/Kbuild
+++ b/Kbuild
@@ -812,6 +812,7 @@
 		$(QDF_LINUX_OBJ_DIR)/qdf_threads.o \
 		$(QDF_LINUX_OBJ_DIR)/qdf_crypto.o \
 		$(QDF_LINUX_OBJ_DIR)/qdf_trace.o \
+		$(QDF_OBJ_DIR)/qdf_str.o \
 		$(QDF_OBJ_DIR)/qdf_types.o
 
 ifeq ($(CONFIG_WLAN_DEBUGFS), y)