intel: fix memory leak related to brw_nir_create_passthrough_tcs()

intel: fix memory leak related to brw_nir_create_passthrough_tcs()

Indeed, the parameter "mem_ctx" was not processed.

For instance, this issue is triggered with the crocus driver and
"piglit/bin/shader_runner tests/spec/arb_tessellation_shader/execution/compatibility/tes-clip-vertex-different-from-position.shader_test -auto -fbo":
SUMMARY: AddressSanitizer: 235216 byte(s) leaked in 48 allocation(s).

Fixes: 96ba0344db8f ("intel: Use common helpers for TCS passthrough shaders")
Signed-off-by: Patrick Lerda <patrick9876@free.fr>
Reviewed-by: Emma Anholt <emma@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22173>