mesa/ff_shader: Fix sampler state reading

mesa/ff_shader: Fix sampler state reading

Fixed function fragment shader generator was incorrectly read texture
sampling state directly from texture object. To make sure that
ARB_sampler_object works correctly shader generator has to use the
bound sampler if one exist.

Signed-off-by: Pauli Nieminen <pauli.nieminen@linux.intel.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Eric Anholt <eric@anholt.net>