vfio/pci: fix memory leaks in alloc_perm_bits()

vfio_pci_disable() calls vfio_config_free() but forgets to call
free_perm_bits() resulting in memory leaks,

unreferenced object 0xc000000c4db2dee0 (size 16):
  comm "qemu-kvm", pid 4305, jiffies 4295020272 (age 3463.780s)
  hex dump (first 16 bytes):
    00 00 ff 00 ff ff ff ff ff ff ff ff ff ff 00 00  ................
  backtrace:
    [<00000000a6a4552d>] alloc_perm_bits+0x58/0xe0 [vfio_pci]
    [<00000000ac990549>] vfio_config_init+0xdf0/0x11b0 [vfio_pci]
    init_pci_cap_msi_perm at drivers/vfio/pci/vfio_pci_config.c:1125
    (inlined by) vfio_msi_cap_len at drivers/vfio/pci/vfio_pci_config.c:1180
    (inlined by) vfio_cap_len at drivers/vfio/pci/vfio_pci_config.c:1241
    (inlined by) vfio_cap_init at drivers/vfio/pci/vfio_pci_config.c:1468
    (inlined by) vfio_config_init at drivers/vfio/pci/vfio_pci_config.c:1707
    [<000000006db873a1>] vfio_pci_open+0x234/0x700 [vfio_pci]
    [<00000000630e1906>] vfio_group_fops_unl_ioctl+0x8e0/0xb84 [vfio]
    [<000000009e34c54f>] ksys_ioctl+0xd8/0x130
    [<000000006577923d>] sys_ioctl+0x28/0x40
    [<000000006d7b1cf2>] system_call_exception+0x114/0x1e0
    [<0000000008ea7dd5>] system_call_common+0xf0/0x278
unreferenced object 0xc000000c4db2e330 (size 16):
  comm "qemu-kvm", pid 4305, jiffies 4295020272 (age 3463.780s)
  hex dump (first 16 bytes):
    00 ff ff 00 ff ff ff ff ff ff ff ff ff ff 00 00  ................
  backtrace:
    [<000000004c71914f>] alloc_perm_bits+0x44/0xe0 [vfio_pci]
    [<00000000ac990549>] vfio_config_init+0xdf0/0x11b0 [vfio_pci]
    [<000000006db873a1>] vfio_pci_open+0x234/0x700 [vfio_pci]
    [<00000000630e1906>] vfio_group_fops_unl_ioctl+0x8e0/0xb84 [vfio]
    [<000000009e34c54f>] ksys_ioctl+0xd8/0x130
    [<000000006577923d>] sys_ioctl+0x28/0x40
    [<000000006d7b1cf2>] system_call_exception+0x114/0x1e0
    [<0000000008ea7dd5>] system_call_common+0xf0/0x278

Fixes: 89e1f7d4 ("vfio: Add PCI device driver")
Signed-off-by: Qian Cai <cai@lca.pw>
[aw: rolled in follow-up patch]
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>