target: msmzirc: Use chip serial to populate device serial number

MDM targets did not have a unique serial number. This change will read
chip serial from SMEM.

Change-Id: I4b466aa2c3b6d50ea7f7c111d3d7d49615ed4359
diff --git a/target/msmzirc/init.c b/target/msmzirc/init.c
index 22e03df..7269278 100644
--- a/target/msmzirc/init.c
+++ b/target/msmzirc/init.c
@@ -200,6 +200,13 @@
 	board->baseband = BASEBAND_MSM;
 }
 
+void target_serialno(unsigned char *buf)
+{
+	uint32_t serialno;
+	serialno = board_chip_serial();
+	snprintf((char *)buf, 13, "%x", serialno);
+}
+
 unsigned check_reboot_mode(void)
 {
 	unsigned restart_reason = 0;