net:sfc: fix non-freed irq in legacy irq mode

SFC driver can be configured via modparam to work using MSI-X, MSI or
legacy IRQ interrupts. In the last one, the interrupt was not properly
released on module remove.

It was not freed because the flag irqs_hooked was not set during
initialization in the case of using legacy IRQ.

Example of (trimmed) trace during module remove without this fix:

remove_proc_entry: removing non-empty directory 'irq/125', leaking at least '0000:3b:00.1'
WARNING: CPU: 39 PID: 3658 at fs/proc/generic.c:715 remove_proc_entry+0x15c/0x170
...trimmed...
Call Trace:
 unregister_irq_proc+0xe3/0x100
 free_desc+0x29/0x70
 irq_free_descs+0x47/0x70
 mp_unmap_irq+0x58/0x60
 acpi_unregister_gsi_ioapic+0x2a/0x40
 acpi_pci_irq_disable+0x78/0xb0
 pci_disable_device+0xd1/0x100
 efx_pci_remove+0xa1/0x1e0 [sfc]
 pci_device_remove+0x38/0xa0
 __device_release_driver+0x177/0x230
 driver_detach+0xcb/0x110
 bus_remove_driver+0x58/0xd0
 pci_unregister_driver+0x2a/0xb0
 efx_exit_module+0x24/0xf40 [sfc]
 __do_sys_delete_module.constprop.0+0x171/0x280
 ? exit_to_user_mode_prepare+0x83/0x1d0
 do_syscall_64+0x3d/0x80
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7f9f9385800b
...trimmed...
Signed-off-by: Íñigo Huguet <ihuguet@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/sfc/nic.c

@@ -90,6 +90,7 @@ int efx_nic_init_interrupt(struct efx_nic *efx)
 				  efx->pci_dev->irq);
 			goto fail1;
 		}
+		efx->irqs_hooked = true;
 		return 0;
 	}