[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/Target/Mips/MipsSEISelLowering.cpp b/llvm/lib/Target/Mips/MipsSEISelLowering.cpp
index f28e8b3..69162d4f 100644
--- a/llvm/lib/Target/Mips/MipsSEISelLowering.cpp
+++ b/llvm/lib/Target/Mips/MipsSEISelLowering.cpp
@@ -3628,7 +3628,7 @@
   MachineInstrBuilder MIB =
       BuildMI(*BB, MI, DL, TII->get(UsingMips32 ? Mips::LH : Mips::LH64), Rt);
   for (unsigned i = 1; i < MI.getNumOperands(); i++)
-    MIB.addOperand(MI.getOperand(i));
+    MIB.add(MI.getOperand(i));
 
   BuildMI(*BB, MI, DL, TII->get(Mips::FILL_H), Wd).addReg(Rt);