i965: Shrink stage_prog_data param array length

i965: Shrink stage_prog_data param array length

It appears we were over-allocating these arrays.

Previously we would use nir->num_uniforms directly for scalar
programs, and multiply it by 4 for vec4 programs.

Instead we should have been dividing by 4 in both cases to convert
from bytes to a gl_constant_value count. The size of gl_constant_value
is 4 bytes.

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>