PCI: endpoint: pci-epf-test: Clean up pci_epf_test_unbind()

PCI: endpoint: pci-epf-test: Clean up pci_epf_test_unbind()

Clean up pci_epf_test_unbind() by using a continue if we did not allocate
memory for the BAR index. This reduces the indentation level by one.

This makes pci_epf_test_unbind() more similar to pci_epf_test_set_bar().

Link: https://lore.kernel.org/linux-pci/20240320113157.322695-6-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>