platform: msm_shared: Use appendprop API to append the bootargs.

Use appendprop_string API to append the bootargs. This
would not override the bootargs if they are already defined
in the DT.

Change-Id: I60a83110770106839962d8f257f756c27ea40fc0
diff --git a/platform/msm_shared/dev_tree.c b/platform/msm_shared/dev_tree.c
index e4505d4..abba3bd 100644
--- a/platform/msm_shared/dev_tree.c
+++ b/platform/msm_shared/dev_tree.c
@@ -823,7 +823,7 @@
 
 	offset = ret;
 	/* Adding the cmdline to the chosen node */
-	ret = fdt_setprop_string(fdt, offset, (const char*)"bootargs", (const void*)cmdline);
+	ret = fdt_appendprop_string(fdt, offset, (const char*)"bootargs", (const void*)cmdline);
 	if (ret)
 	{
 		dprintf(CRITICAL, "ERROR: Cannot update chosen node [bootargs]\n");