mesa: do not skip att and spot calculation for infinite light

mesa: do not skip att and spot calculation for infinite light

glspec doesn't say that we should skip the attenuation and spot
calculation for infinite light(Ppli.w == 0). Instead, it gives a same
formula to do the light calculation for both finite light and infinite
light(see page 62 of glspec 2.1.pdf)

Also from the formula (2.4) at page 62 of glspec 2.1.pdf, we can skip
attenuation calculation if Ppli.w == 0.

This would fix all the intel oglc l_sed fail subcases and introduces no
intel oglc regressions.

v2: fix an wrong intendation(comments from Brian).

Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Acked-by: Brian Paul <brianp@vmware.com>