PCI: cadence: Check for the existence of cdns_pcie::ops before using it

PCI: cadence: Check for the existence of cdns_pcie::ops before using it

cdns_pcie::ops might not be populated by all the Cadence glue drivers. This
is going to be true for the upcoming Sophgo platform which doesn't set the
ops.

Hence, add a check to prevent NULL pointer dereference.

Signed-off-by: Chen Wang <unicorn_wang@outlook.com>
[mani: reworded subject and description]
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Link: https://patch.msgid.link/35182ee1d972dfcd093a964e11205efcebbdc044.1757643388.git.unicorn_wang@outlook.com