bpfloader - minor fixups asked for by reviewer

As requested by Bernie on previous commit.

Bug: 190519702
Test: atest, TreeHugger - existing bpf programs load
  examination of bpfloader logs
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I4f5181f371d31dcf52768217ffd2b1b5b772103d
diff --git a/libbpf_android/Loader.cpp b/libbpf_android/Loader.cpp
index c10988d..b1af34f 100644
--- a/libbpf_android/Loader.cpp
+++ b/libbpf_android/Loader.cpp
@@ -514,14 +514,14 @@
         if (BPFLOADER_VERSION < md[i].bpfloader_min_ver) {
             ALOGI("skipping map %s which requires bpfloader min ver 0x%05x\n", mapNames[i].c_str(),
                   md[i].bpfloader_min_ver);
-            mapFds.push_back(std::move(fd));  // -1
+            mapFds.push_back(unique_fd());
             continue;
         }
 
         if (BPFLOADER_VERSION >= md[i].bpfloader_max_ver) {
             ALOGI("skipping map %s which requires bpfloader max ver 0x%05x\n", mapNames[i].c_str(),
                   md[i].bpfloader_max_ver);
-            mapFds.push_back(std::move(fd));  // -1
+            mapFds.push_back(unique_fd());
             continue;
         }