gallium/u_threaded_context: don't call memcpy in tc_set_constant_buffer

In sysprof, the CPU time spend in tc_set_constant_buffer drops
from 7% to 1.4% in a release build. It doesn't make sense to me.

Reviewed-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6952>
1 file changed