mesa: Makefile.sources: Add ir3_nir_lower_load_barycentric_at_sample/offset to Makefi...

mesa: Makefile.sources: Add ir3_nir_lower_load_barycentric_at_sample/offset to Makefile.sources

In commit 2f0b9d22495 ("freedreno/ir3: lower
load_barycentric_at_offset") a new file was added that needs to
also be added to the Makefile.sources list used by Android and
SCons build system.

Cc: Rob Clark <robdclark@chromium.org>
Cc: Emil Velikov <emil.l.velikov@gmail.com>
Cc: Amit Pundir <amit.pundir@linaro.org>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Alistair Strachan <astrachan@google.com>
Cc: Greg Hartman <ghartman@google.com>
Cc: Tapani Pälli <tapani.palli@intel.com>
Cc: Jason Ekstrand <jason@jlekstrand.net>
Fixes: 2f0b9d22495 ("freedreno/ir3: lower load_barycentric_at_offset")
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>