scsi: sni_53c710: Add IRQ check

The driver neglects to check the result of platform_get_irq()'s call and
blithely passes the negative error codes to request_irq() (which takes
*unsigned* IRQ #s), causing it to fail with -EINVAL (overridden by -ENODEV
further below).  Stop calling request_irq() with the invalid IRQ #s.

Link: https://lore.kernel.org/r/8f4b8fa5-8251-b977-70a1-9099bcb4bb17@omprussia.ru


Fixes: c27d85f3 ("[SCSI] SNI RM 53c710 driver")
Signed-off-by: Sergey Shtylyov <s.shtylyov@omprussia.ru>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>