liquidio: fix implicit irq include causing build failures

To fix

In file included from drivers/net/ethernet/cavium/liquidio/octeon_mem_ops.c:24:0:
drivers/net/ethernet/cavium/liquidio/octeon_device.h:216:2: error: expected specifier-qualifier-list before ‘irqreturn_t’
  irqreturn_t (*process_interrupt_regs)(void *);
  ^

as seen on arm64 allmodconfig builds.

Cc: Derek Chickles <derek.chickles@caviumnetworks.com>
Cc: Satanand Burla <satananda.burla@caviumnetworks.com>
Cc: Felix Manlunas <felix.manlunas@caviumnetworks.com>
Cc: Raghu Vatsavayi <raghu.vatsavayi@caviumnetworks.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>