[NFC][Regalloc] accessors for 'reg' and 'weight'

Also renamed the fields to follow style guidelines.

Accessors help with readability - weight mutation, in particular,
is easier to follow this way.

Differential Revision: https://reviews.llvm.org/D87725
diff --git a/llvm/lib/CodeGen/LiveIntervalUnion.cpp b/llvm/lib/CodeGen/LiveIntervalUnion.cpp
index 43fa8f2..cccc14e 100644
--- a/llvm/lib/CodeGen/LiveIntervalUnion.cpp
+++ b/llvm/lib/CodeGen/LiveIntervalUnion.cpp
@@ -85,8 +85,8 @@
     return;
   }
   for (LiveSegments::const_iterator SI = Segments.begin(); SI.valid(); ++SI) {
-    OS << " [" << SI.start() << ' ' << SI.stop() << "):"
-       << printReg(SI.value()->reg, TRI);
+    OS << " [" << SI.start() << ' ' << SI.stop()
+       << "):" << printReg(SI.value()->reg(), TRI);
   }
   OS << '\n';
 }
@@ -95,7 +95,7 @@
 // Verify the live intervals in this union and add them to the visited set.
 void LiveIntervalUnion::verify(LiveVirtRegBitSet& VisitedVRegs) {
   for (SegmentIter SI = Segments.begin(); SI.valid(); ++SI)
-    VisitedVRegs.set(SI.value()->reg);
+    VisitedVRegs.set(SI.value()->reg());
 }
 #endif //!NDEBUG