ac/nir,radv,radeonsi/nir: use correct indices for interpolation intrinsics

ac/nir,radv,radeonsi/nir: use correct indices for interpolation intrinsics

Fixes artifacts in World of Warcraft when Multi-sample Alpha-Test is
enabled with DXVK.
It also fixes artifacts with Fallout 4's god rays with DXVK.
Various piglit interpolateAt*() tests under NIR are also fixed.

v2: formatting fix
    update commit message to include Fallout 4 and the Fixes tag

Fixes: f4e499ec791 ('radv: add initial non-conformant radv vulkan driver')
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=106595
Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>