r600: double multiply can handle only one multiply at a time

It seems clear that trying to multiply two pairs of doubles would result
in the temporary register getting overwritten by the second pair. So
make the code more explicit.

Tested-by: Glenn Kennard <glenn.kennard@gmail.com>
Tested-by: James Harvey <lothmordor@gmail.com>
Cc: 17.0 <mesa-stable@lists.freedesktop.org>
(cherry picked from commit 76b02d2fe1df5351f67f53d07b37952043f0a84c)
1 file changed