i965: Don't leak the IR annotation into later instructions.

i965: Don't leak the IR annotation into later instructions.

After walking our IR instructions (Mesa or GLSL), we don't want to also
mark the start of the FB/URB writes or whatever as being that IR.  This
can end up being misleading when the end of the IR visit got copy
propagated out to a later instruction in the URB writes.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>