tgsi_to_nir: Translate TGSI_INTERPOLATE_COLOR as INTERP_MODE_NONE

tgsi_to_nir: Translate TGSI_INTERPOLATE_COLOR as INTERP_MODE_NONE

Translating TGSI_INTERPOLATE_COLOR as INTERP_MODE_SMOOTH made
it for drivers impossible to have flatshaded color inputs.

Translate it to INTERP_MODE_NONE which drivers interpret as
smooth or flat depending on flatshading state.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=111467

Fixes: 770faf54 ("tgsi_to_nir: Improve interpolation modes.")
Signed-off-by: Danylo Piliaiev <danylo.piliaiev@globallogic.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Eric Anholt <eric@anholt.net>