ioat: Use pci_enable_msix_exact() instead of pci_enable_msix()

As result of deprecation of MSI-X/MSI enablement functions
pci_enable_msix() and pci_enable_msi_block() all drivers
using these two interfaces need to be updated to use the
new pci_enable_msi_range()  or pci_enable_msi_exact()
and pci_enable_msix_range() or pci_enable_msix_exact()
interfaces.

Function pci_enable_msix() returns a tri-state value while
pci_enable_msi_exact() is a canonical zero/-errno variant.
The former is being phased out in favor of the latter.
In case of 'ioat' there (should be) no difference.

Cc: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>