x86: SGI UV: Fix BAU initialization

A memory mapped register that affects the SGI UV Broadcast
Assist Unit's interrupt handling may sometimes be unintialized.

Remove the condition on its initialization, as that condition
can be randomly satisfied by a hardware reset.

Signed-off-by: Cliff Wickman <cpw@sgi.com>
Cc: <stable@kernel.org>
LKML-Reference: <E1NBGB9-0005nU-Dp@eag09.americas.sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>