[CodeGen] Rename MachineInstrBuilder::addOperand. NFC

Rename from addOperand to just add, to match the other method that has been
added to MachineInstrBuilder for adding more than just 1 operand.

See https://reviews.llvm.org/D28057 for the whole discussion.

Differential Revision: https://reviews.llvm.org/D28556

llvm-svn: 291891
diff --git a/llvm/lib/CodeGen/ImplicitNullChecks.cpp b/llvm/lib/CodeGen/ImplicitNullChecks.cpp
index 9588dfb..0440555 100644
--- a/llvm/lib/CodeGen/ImplicitNullChecks.cpp
+++ b/llvm/lib/CodeGen/ImplicitNullChecks.cpp
@@ -522,7 +522,7 @@
                  .addImm(LoadMI->getOpcode());
 
   for (auto &MO : LoadMI->uses())
-    MIB.addOperand(MO);
+    MIB.add(MO);
 
   MIB.setMemRefs(LoadMI->memoperands_begin(), LoadMI->memoperands_end());