tgsi_to_nir: Fix the TGSI ARR translation by converting the result to int.

tgsi_to_nir: Fix the TGSI ARR translation by converting the result to int.

According to the TGSI spec, ARR needs to do a rounding and then
a float-to-integer conversion which was missing. This patch also
makes the rounding a bit more efficient by using nir_fround_even
instead of the previous nir_ffloor+nir_fadd trick.

Signed-Off-By: Timur Kristóf <timur.kristof@gmail.com>
Tested-by: Andre Heider <a.heider@gmail.com>
Tested-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>