SCSI: ARM: ncr5380/oak uses no interrupts

The ncr5380 driver is included by multiple board specific
drivers, which may or may not use the interrupt handler.
The oak variant doesn't, and should set the DONT_USE_INTR
macro.

Without this patch, building rpc_defconfig results in:

drivers/scsi/arm/../NCR5380.c:1160:20: warning: 'oakscsi_intr' defined but not used [-Wunused-function]

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Cc: "James E.J. Bottomley" <JBottomley@parallels.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-scsi@vger.kernel.org