[SPARC64]: Fix SBUS IRQ regression caused by PCI-E driver.

We used to access the 64-bit IRQ IMAP and ICLR registers of bus
controllers 4-bytes in and as a 32-bit register word, since only the
low 32-bits were relevant.  This seemed like a good idea at the time.

But the PCI-E controller requires full 8-byte 64-bit access to
these registers, so we switched over to accessing them fully.

SBUS was not adjusted properly, which broke interrupts completely.

Signed-off-by: David S. Miller <davem@davemloft.net>