MIPS: SNI: Fix SCSI interrupt

On RM400(a20r) machines ISA and SCSI interrupts share the same interrupt
line. Commit 49e6e07e ("MIPS: pass non-NULL dev_id on shared
request_irq()") accidently dropped the IRQF_SHARED bit, which breaks
registering SCSI interrupt. Put back IRQF_SHARED and add dev_id for
ISA interrupt.

Fixes: 49e6e07e ("MIPS: pass non-NULL dev_id on shared request_irq()")
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>