[AMDGPU] fix MADAK/MADMK instructions operand namings to match encoding fields.

$vsrc1 -> $src1, $k -> $imm

Differential Revision: http://reviews.llvm.org/D18659

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@265141 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed