i965: Use a UW source type for CS_OPCODE_CS_TERMINATE.

i965: Use a UW source type for CS_OPCODE_CS_TERMINATE.

SIMD16 compute shaders use a send(16) with mlen 1 for the EOT message,
using a source of g127 for the single register.  With a UD type, this
supposedly could read g128, which doesn't exist, causing the simulator
to get cranky.  Use a UW type to avoid this.

Cc: "17.0" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Francisco Jerez <currojerez@riseup.net>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>