trunks_send: fix compiling error of comparing int and uint_32.

This is specific to reef factory branch not from original CLs stack. It
seems the compile options here treated warning as error so can't compile
trunks_send without this fix.

BUG=b:73256785
TEST=Locally compile trunks_send succesfully.

Change-Id: I6403fd654c088db1fbd7113a7e5377e86acb510d
diff --git a/trunks/trunks_send.cc b/trunks/trunks_send.cc
index 37609d0..7d2a124 100644
--- a/trunks/trunks_send.cc
+++ b/trunks/trunks_send.cc
@@ -352,7 +352,7 @@
   rpdu->backup_ro_offset = base::NetToHost32(rpdu->backup_ro_offset);
   rpdu->backup_rw_offset = base::NetToHost32(rpdu->backup_rw_offset);
 
-  for (int i = 0; i < arraysize(FirstResponsePdu::shv); i++) {
+  for (uint32_t i = 0; i < arraysize(FirstResponsePdu::shv); i++) {
     rpdu->shv[i].minor = base::NetToHost32(rpdu->shv[i].minor);
     rpdu->shv[i].major = base::NetToHost32(rpdu->shv[i].major);
     rpdu->shv[i].epoch = base::NetToHost32(rpdu->shv[i].epoch);
@@ -468,7 +468,7 @@
   //
 
   index = section_offsets[0] > section_offsets[1] ? 1 : 0;
-  for (int i = 0; i < arraysize(section_offsets); i++) {
+  for (uint32_t i = 0; i < arraysize(section_offsets); i++) {
     if (!TransferSection(proxy, update_image, section_offsets[index],
                          rpdu.shv[index], force)) {
       if (!force) {