platform: msm_shared: check if cmdline is NULL before using it

Pointer 'final_cmdline' returned from call to function
'update_cmdline' may be NULL, will be passed to function
and may be dereferenced there by passing argument 2 to
function 'update_device_tree'.

Change-Id: I6cd52dd9b7799f0ecb3fc863497647ad653a5e9d
CRs-Fixed: 687723
diff --git a/platform/msm_shared/dev_tree.c b/platform/msm_shared/dev_tree.c
index 5df5a70..07c99ff 100644
--- a/platform/msm_shared/dev_tree.c
+++ b/platform/msm_shared/dev_tree.c
@@ -822,12 +822,15 @@
 	}
 
 	offset = ret;
-	/* Adding the cmdline to the chosen node */
-	ret = fdt_appendprop_string(fdt, offset, (const char*)"bootargs", (const void*)cmdline);
-	if (ret)
+	if (cmdline)
 	{
-		dprintf(CRITICAL, "ERROR: Cannot update chosen node [bootargs]\n");
-		return ret;
+		/* Adding the cmdline to the chosen node */
+		ret = fdt_appendprop_string(fdt, offset, (const char*)"bootargs", (const void*)cmdline);
+		if (ret)
+		{
+			dprintf(CRITICAL, "ERROR: Cannot update chosen node [bootargs]\n");
+			return ret;
+		}
 	}
 
 	if (ramdisk_size) {