aco/optimizer: fix incorrect operand order assumption for neg(mul) opt

The code that labels instructions doesn't care about the order either.

Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/14013
Cc: mesa-stable

Reviewed-by: Timur Kristóf <timur.kristof@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/37643>
(cherry picked from commit 9533e7cdae4722e306708624ace4226a6ab0dcdd)

[Eric: the backport includes an extra swap of two conditions, as
 recommended by Rhys to work around an issue with old compilers:
 https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/37643#note_3137704]