st/glsl_to_nir: Calculate num_uniforms from NumParameterValues

st/glsl_to_nir: Calculate num_uniforms from NumParameterValues

We don't need to determine the number of uniform slots here, it's
already available as prog->Parameters->NumParameterValues.  The way we
previously determined the number of slots was also broken for
PackedDriverUniformStorage, where we would add loc (in dwords) and
type_size() (in vec4s).

Signed-off-by: Kristian H. Kristensen <hoegsberg@chromium.org>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Rob Clark <robdclark@gmail.com>