ahci: Use pci_enable_msi_exact() instead of pci_enable_msi_range()

The driver calls pci_enable_msi_range() function with the range of
[nvec..nvec] which is what pci_enable_msi_exact() function is for.

Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
Cc: linux-ide@vger.kernel.org
Signed-off-by: Tejun Heo <tj@kernel.org>