Rename memrr ptrreg and offreg components.

Currently, the sub-operand of a memrr address that corresponds to what
hardware considers the base register is called "offreg", while the
sub-operand that corresponds to the offset is called "ptrreg".

To avoid confusion, this patch simply swaps the named of those two
sub-operands and updates all uses.  No functional change is intended.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@177734 91177308-0d34-0410-b5e6-96231b3b80d8