i965/fs/skl+: Fix calculating gl_SampleID for 16x MSAA

In order to accomodate 16x MSAA, the starting sample pair index is now
3 bits rather than 2 on SKL+.

Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>
1 file changed