staging: octeon-ethernet: fix build errors by including interrupt.h

This patch fixes the following build failures:

drivers/staging/octeon/ethernet.c: In function 'cvm_oct_cleanup_module':
drivers/staging/octeon/ethernet.c:799:2: error: implicit declaration of function 'free_irq'
drivers/staging/octeon/ethernet-rx.c: In function 'cvm_oct_no_more_work':
drivers/staging/octeon/ethernet-rx.c:119:3: error: implicit declaration of function 'enable_irq'
drivers/staging/octeon/ethernet-rx.c: In function 'cvm_oct_do_interrupt':
drivers/staging/octeon/ethernet-rx.c:136:2: error: implicit declaration of function 'disable_irq_nosync'
drivers/staging/octeon/ethernet-rx.c: In function 'cvm_oct_rx_initialize':
drivers/staging/octeon/ethernet-rx.c:532:2: error: implicit declaration of function 'request_irq'
drivers/staging/octeon/ethernet-tx.c: In function 'cvm_oct_tx_initialize':
drivers/staging/octeon/ethernet-tx.c:712:2: error: implicit declaration of function 'request_irq'
drivers/staging/octeon/ethernet-tx.c: In function 'cvm_oct_tx_shutdown':
drivers/staging/octeon/ethernet-tx.c:723:2: error: implicit declaration of function 'free_irq'

Signed-off-by: Imre Kaloz <kaloz@openwrt.org>
Acked-by: David Daney <david.daney@cavium.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>