e1000e: restore call to pci_clear_master()

In attempting to resolve a minor merge conflict, commit e5f2ef7a
(Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net

) accidentally
dropped a call to pci_clear_master() that was intended to remain in place.

Commit 4e0855df (e1000e: fix pci-device enable-counter balance)
replaced a call to pci_disable_device() by one to pci_clear_master(). And then
commit 66148bab (e1000e: fix runtime power management transitions)
deleted a number of lines starting two lines following that call.

This patch restores the call to pci_clear_master() in __e1000_shutdown().

v2: added summary lines (enclosed in parens) following commit IDs

Signed-off-by: Dean Nelson <dnelson@redhat.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Acked-by: Bruce Allan <bruce.w.allan@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>