i965: Make the CONT instruction point to the WHILE instruction.

i965: Make the CONT instruction point to the WHILE instruction.

This fixes piglit test glsl-fs-loop-continue.shader_test on Ivybridge.
According to the documentation, the CONT instruction's UIP field should
point to the WHILE instruction on both Sandybridge and Ivybridge.

The previous code made UIP point to the implicit DO instruction, which
seems incorrect.  I'm not sure how it could have worked on Sandybridge.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>