vfio/pci: Fix vfio_rtl8168_quirk_data_read address offset

vfio/pci: Fix vfio_rtl8168_quirk_data_read address offset

Introductory comment for rtl8168 VFIO MSI-X quirk states:
At BAR2 offset 0x70 there is a dword data register,
         offset 0x74 is a dword address register.
vfio: vfio_bar_read(0000:05:00.0:BAR2+0x70, 4) = 0xfee00398 // read data

Thus, correct offset for data read is 0x70,
but function vfio_rtl8168_quirk_data_read() wrongfully uses offset 0x74.

Signed-off-by: Thorsten Kohfeldt <thorsten.kohfeldt@gmx.de>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>