i965/vec4/gen8: Handle the MUL dest hazard exception

i965/vec4/gen8: Handle the MUL dest hazard exception

Fix one of the few cases where we can't reliable touch the destination hazard
bits. I am explicitly doing this patch individually so it is easy to backport. I
was tempted to do this patch before the previous patch which reorganized the
code, but I believe even doing that first, this is still easy to backport.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=84212
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Matt Turner <mattst88@gmail.com>