tgsi_to_nir: Set correct location for uniforms.

tgsi_to_nir: Set correct location for uniforms.

Previously, only the driver_location was set for all variables,
but constants need to use the location field instead. This change
is necessary because the nine state tracker can produce non-packed
constants whose location needs to be explicitly set.

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: Timothy Arceri <tarceri@itsqueeze.com>