intel/fs: copy instruction sources in logical send lowering

intel/fs: copy instruction sources in logical send lowering

Having references to inst->src[X] when you're also modifying
inst->src[X] is a receipe for disaster. Making changes to the lowering
code I've been bitten quite a few times by this take copies of all
sources to do the lowering.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Francisco Jerez <currojerez@riseup.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21853>