spirv: Apply OriginUpperLeft to FragCoord

This behaviour was changed in 1e5b09f42f694687ac. The commit message
for that says it is just a “tidy up” so my assumption is that the
behaviour change was a mistake. It’s a little hard to decipher looking
at the diff, but the previous code before that patch was:

  if (builtin == SpvBuiltInFragCoord || builtin == SpvBuiltInSamplePosition)
     nir_var->data.origin_upper_left = b->origin_upper_left;

  if (builtin == SpvBuiltInFragCoord)
     nir_var->data.pixel_center_integer = b->pixel_center_integer;

After the patch the code was:

  case SpvBuiltInSamplePosition:
     nir_var->data.origin_upper_left = b->origin_upper_left;
     /* fallthrough */
  case SpvBuiltInFragCoord:
     nir_var->data.pixel_center_integer = b->pixel_center_integer;
     break;

Before the patch origin_upper_left affected both builtins and
pixel_center_integer only affected FragCoord. After the patch
origin_upper_left only affects SamplePosition and pixel_center_integer
affects both variables.

This patch tries to restore the previous behaviour by changing the
code to:

  case SpvBuiltInFragCoord:
     nir_var->data.pixel_center_integer = b->pixel_center_integer;
     /* fallthrough */
  case SpvBuiltInSamplePosition:
     nir_var->data.origin_upper_left = b->origin_upper_left;
     break;

This change will be important for ARB_gl_spirv which is meant to
support OriginLowerLeft.

Reviewed-by: Jason Ekstrand <[email protected]>
Reviewed-by: Anuj Phogat <[email protected]>
Fixes: 1e5b09f42f694687ac "spirv: Tidy some repeated if checks..."

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