IB/qib: Clean up unnecessary MSI/MSI-X capability find

PCI core will initialize device MSI/MSI-X capability in
pci_msi_init_pci_dev().  So device drivers should use
pci_dev->msi_cap/msix_cap to determine whether a device supports
MSI/MSI-X instead of using pci_find_capability(pci_dev,
PCI_CAP_ID_MSI/MSIX).  Access to PCIe device config space again will
consume more time.

Signed-off-by: Yijing Wang <wangyijing@huawei.com>
Acked-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>