i965: Handle ir_triop_csel in emit_if_gen6().

i965: Handle ir_triop_csel in emit_if_gen6().

ir_triop_csel can return a boolean expression, so we need to handle it
here; we simply forgot when we added ir_triop_csel, and forgot again
when adding it to emit_bool_to_cond_code.

Fixes Piglit's EXT_shader_integer_mix/{vs,fs}-mix-if-bool on Sandybridge.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Cc: mesa-stable@lists.freedesktop.org