[scudo] Use the unmap function on MemMap object. (#204001)

The current call does a unmap(MemMap), but the rest of the code is doing
MemMap.unmap(XXX), so follow that pattern.

GitOrigin-RevId: b2cb99971fb498a7ff458b3a1a4a4edf3c3bafd3

secondary.h

diff --git a/secondary.h b/secondary.h
index a689ea9..26c45cc 100644
--- a/secondary.h
+++ b/secondary.h
@@ -906,7 +906,7 @@
   const uptr AllocPos = roundDown(CommitBase + CommitSize - Size, Alignment);
   if (!mapSecondary<Config>(Options, CommitBase, CommitSize, AllocPos, 0,
                             MemMap)) {
-    unmap(MemMap);
+    MemMap.unmap();
     return nullptr;
   }
   const uptr HeaderPos = AllocPos - getHeadersSize();