boot_serial: Adapt to zcbor 0.8.x

Change one _term to _lit that was missed earlier.

Signed-off-by: Øyvind Rønningstad <oyvind.ronningstad@nordicsemi.no>
diff --git a/boot/boot_serial/src/boot_serial.c b/boot/boot_serial/src/boot_serial.c
index fe79d3d..b631e15 100644
--- a/boot/boot_serial/src/boot_serial.c
+++ b/boot/boot_serial/src/boot_serial.c
@@ -934,7 +934,7 @@
     }
 
     zcbor_map_start_encode(cbor_state, 10);
-    zcbor_tstr_put_term(cbor_state, "r");
+    zcbor_tstr_put_lit(cbor_state, "r");
     if (zcbor_tstr_encode(cbor_state, &value) && zcbor_map_end_encode(cbor_state, 10)) {
         boot_serial_output();
         return;