PCI: endpoint: pci-epf-test: Simplify pci_epf_test_set_bar() loop

PCI: endpoint: pci-epf-test: Simplify pci_epf_test_set_bar() loop

Simplify the loop in pci_epf_test_set_bar().
If we allocated memory for the BAR, we need to call set_bar() for that
BAR, if we did not allocated memory for that BAR, we need to skip.
It is as simple as that. This also matches the logic in
pci_epf_test_unbind().

A 64-bit BAR will still only be one allocation, with the BAR succeeding
the 64-bit BAR being null.

While at it, remove the misleading comment.
A EPC .set_bar() callback should never change the epf_bar->flags.
(E.g. to set a 64-bit BAR if we requested a 32-bit BAR.)

A .set_bar() callback should do what we request it to do.
If it can't satisfy the request, it should return an error.

If platform has a specific requirement, e.g. that a certain BAR has to
be a 64-bit BAR, then it should specify that by setting the .only_64bit
flag for that specific BAR in epc_features->bar[], such that
pci_epf_alloc_space() will return a epf_bar with the 64-bit flag set.
(Such that .set_bar() will receive a request to set a 64-bit BAR.)

Link: https://lore.kernel.org/linux-pci/20240320113157.322695-5-cassel@kernel.org
Signed-off-by: Niklas Cassel <cassel@kernel.org>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>