sfc: avoid double pci_remove of VFs

sfc: avoid double pci_remove of VFs

If pci_remove was called for a PF with VFs, the removal of the VFs was
called twice from efx_ef10_sriov_fini: one directly with pci_driver->remove
and another implicit by calling pci_disable_sriov, which also perform
the VFs remove. This was leading to crashing the kernel on the second
attempt.

Given that pci_disable_sriov already calls to pci remove function, get
rid of the direct call to pci_driver->remove from the driver.

2 different ways to trigger the bug:
- Create one or more VFs, then attach the PF to a virtual machine (at
  least with qemu/KVM)
- Create one or more VFs, then remove the PF with:
  echo 1 > /sys/bus/pci/devices/PF_PCI_ID/remove

Removing sfc module does not trigger the error, at least for me, because
it removes the VF first, and then the PF.

Example of a log with the error:
    list_del corruption, ffff967fd20a8ad0->next is LIST_POISON1 (dead000000000100)
    ------------[ cut here ]------------
    kernel BUG at lib/list_debug.c:47!
    [...trimmed...]
    RIP: 0010:__list_del_entry_valid.cold.1+0x12/0x4c
    [...trimmed...]
    Call Trace:
    efx_dissociate+0x1f/0x140 [sfc]
    efx_pci_remove+0x27/0x150 [sfc]
    pci_device_remove+0x3b/0xc0
    device_release_driver_internal+0x103/0x1f0
    pci_stop_bus_device+0x69/0x90
    pci_stop_and_remove_bus_device+0xe/0x20
    pci_iov_remove_virtfn+0xba/0x120
    sriov_disable+0x2f/0xe0
    efx_ef10_pci_sriov_disable+0x52/0x80 [sfc]
    ? pcie_aer_is_native+0x12/0x40
    efx_ef10_sriov_fini+0x72/0x110 [sfc]
    efx_pci_remove+0x62/0x150 [sfc]
    pci_device_remove+0x3b/0xc0
    device_release_driver_internal+0x103/0x1f0
    unbind_store+0xf6/0x130
    kernfs_fop_write+0x116/0x190
    vfs_write+0xa5/0x1a0
    ksys_write+0x4f/0xb0
    do_syscall_64+0x5b/0x1a0
    entry_SYSCALL_64_after_hwframe+0x65/0xca

Signed-off-by: Íñigo Huguet <ihuguet@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>