The only usage of pci_ep_ops is to assign its address to the ops field
in the dw_pcie_ep struct which is a pointer to const struct dw_pcie_ep_ops.
Make it const to allow the compiler to put it in read-only memory.

Link: https://lore.kernel.org/r/20211204220316.88655-1-rikard.falkeborn@gmail.comSigned-off-by: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Krzysztof Wilczyński <kw@linux.com>