[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/AMDGPU/SIInsertSkips.cpp b/llvm/lib/Target/AMDGPU/SIInsertSkips.cpp
index 91e4bf75..fe14647 100644
--- a/llvm/lib/Target/AMDGPU/SIInsertSkips.cpp
+++ b/llvm/lib/Target/AMDGPU/SIInsertSkips.cpp
@@ -195,8 +195,8 @@
     }
   } else {
     BuildMI(MBB, &MI, DL, TII->get(AMDGPU::V_CMPX_LE_F32_e32))
-      .addImm(0)
-      .addOperand(Op);
+        .addImm(0)
+        .add(Op);
   }
 }