i965: fix varying output setup

i965: fix varying output setup

Since 7f53fead5c we treat every location as using all
four components so we only need special handling for
doubles when they cross multiple locations.

This fixes a crash in GL45-CTS.enhanced_layouts.varying_locations
where the outputs array would overflow when a dmat2 was stored at
the max varying location i.e 30.

Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>