[nrf fromlist] boot_serial: Fix rc not being returned as a signed value

Fixes an issue whereby rc is a signed variable but is returned as
an unsigned variable in the zcbor functions.

Upstream PR: mcu-tools/mcuboot#1538

Signed-off-by: Jamie McCrae <[email protected]>

Author: nordicjm

boot/boot_serial/src/boot_serial.c

@@ -586,7 +586,7 @@ bs_upload(char *buf, int len)
     BOOT_LOG_INF("RX: 0x%x", rc);
     zcbor_map_start_encode(cbor_state, 10);
     zcbor_tstr_put_lit_cast(cbor_state, "rc");
-    zcbor_uint32_put(cbor_state, rc);
+    zcbor_int32_put(cbor_state, rc);
     if (rc == 0) {
         zcbor_tstr_put_lit_cast(cbor_state, "off");
         zcbor_uint32_put(cbor_state, curr_off);
@@ -612,7 +612,7 @@ bs_rc_rsp(int rc_code)
 {
     zcbor_map_start_encode(cbor_state, 10);
     zcbor_tstr_put_lit_cast(cbor_state, "rc");
-    zcbor_uint32_put(cbor_state, rc_code);
+    zcbor_int32_put(cbor_state, rc_code);
     zcbor_map_end_encode(cbor_state, 10);
     boot_serial_output();
 }