PCI: fix access of PCI_X_CMD by pcix get and set mmrbc functions

An e1000 driver on a system with a PCI-X bus was always being returned
a value of 135 from both pcix_get_mmrbc() and pcix_set_mmrbc(). This
value reflects an error return of PCIBIOS_BAD_REGISTER_NUMBER from
pci_bus_read_config_dword(,, cap + PCI_X_CMD,).

This is because for a dword, the following portion of the PCI_OP_READ()
macro:

	if (PCI_##size##_BAD) return PCIBIOS_BAD_REGISTER_NUMBER;

expands to:

	if (pos & 3) return PCIBIOS_BAD_REGISTER_NUMBER;

And is always true for 'cap + PCI_X_CMD', which is 0xe4 + 2 = 0xe6. ('cap' is
the result of calling pci_find_capability(, PCI_CAP_ID_PCIX).)

The same problem exists for pci_bus_write_config_dword(,, cap + PCI_X_CMD,).
In both cases, instead of calling _dword(), _word() should be called.

Cc: stable@kernel.org
Signed-off-by: Dean Nelson <dnelson@redhat.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>