i965/eu: Use current exec size instead of p->compressed in surface message generation.

i965/eu: Use current exec size instead of p->compressed in surface message generation.

This was kind of an abuse of p->compressed, dataport send message
instructions are always uncompressed.  Use the current execution size
instead since p->compressed is on its way out.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>