[SPARC64]: Fix endless loop in cheetah_xcall_deliver().

[ Upsteam commit: 0de56d1a ]

We need to mask out the proper bits when testing the dispatch status
register else we can see unrelated NACK bits from previous cross call
sends.

Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Adrian Bunk <bunk@kernel.org>