glsl/linker: fix multiple streams transform feedback.

glsl/linker: fix multiple streams transform feedback.

e2791b38b42f83add5b07298c39741bf0a6d7d4b
mesa/program_interface_query: fix transform feedback varyings.

caused a regression in
GL45-CTS.gtf40.GL3Tests.transform_feedback3.transform_feedback3_multiple_streams
on radeonsi.

The problem was it was using the skip components varying to set
the stream id, when it should wait until a varying was written,
this just adds the varying checks in the right place.

Cc: "12.0" <mesa-stable@lists.freedesktop.org>
Reviewed-by: Timothy Arceri <timothy.arceri@collabora.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
(cherry picked from commit 1fe7bbb911ac708999685c942e971693b688a334)