PCI MSI: Remove attribute check from pci_disable_msi()

The msi_list never have MSI-X's msi_desc while MSI is enabled,
and also it never have MSI's msi_desc while MSI-X is enabled.

This patch remove check for MSI-X entry from the pci_disable_msi(),
referring that pci_disable_msix() does not have any check for MSI
entry.

Reviewed-by: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>