r600g: Avoid duplicated initialization of TGSI_OPCODE_DFMA

r600g: Avoid duplicated initialization of TGSI_OPCODE_DFMA

As reported by Clang, TGSI_OPCODE_DFMA (defined magic number 118) is
currently initialized twice for Cayman and Evergreen.

When Jan Vesely added double precision FMA opcode it did make sense
to locate it immediately after TGSI_OPCODE_DMAD, although this is
out of order.

This change cleans up the prior magic number definition and ensures
any later reordering of this struct will not create problems.

Prior change was:

  commit 015e2e0fce3eea7884f8df275c2fadc35143a324
  Author: Jan Vesely <jan.vesely@rutgers.edu>
  Date:   Sat Jul 2 16:14:54 2016 -0400

      r600g: Add double precision FMA ops

      Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=96782
      Fixes: 54c4d525da7c7fc1e103d7a3e6db015abb132d5d ("r600g: Enable FMA on chips that support it")
      Signed-off-by: Jan Vesely <jan.vesely@rutgers.edu>
      Tested-by: James Harvey <lothmordor@gmail.com>
      Signed-off-by: Marek Olšák <marek.olsak@amd.com>
Signed-off-by: Rhys Kidd <rhyskidd@gmail.com>
Reviewed-by: Jan Vesely <jan.vesely@rutgers.edu>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Tested-by: James Harvey <lothmordor@gmail.com>