i965/fs: Set the header_size on LOAD_PAYLOAD in opt_sampler_eot

i965/fs: Set the header_size on LOAD_PAYLOAD in opt_sampler_eot

Commit 94ee908448 added a header size parameter to the function to
create the LOAD_PAYLOAD instruction. However this broke
opt_sampler_eot which manually constructs the instruction and so
wasn't setting the header_size. This ends up making the parameters for
the send message all have the wrong location and it all falls apart.

Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.com>
Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>