[llvm] [MC] Use MCRegister::id() to avoid implicit casts. NFC (PR #168233)

[Fangrui Song via llvm-commits]

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@@ -89,7 +89,7 @@ ArrayRef<MCPhysReg> MCRegisterInfo::getCachedAliasesOf(MCRegister R) const {
     return Aliases;
 
   for (MCRegAliasIteratorImpl It(R, this); It.isValid(); ++It)
-    Aliases.push_back(*It);
+    Aliases.push_back((*It).id());
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MaskRay wrote:

`It->id()`

https://github.com/llvm/llvm-project/pull/168233