PCI: Simplify pcie_capability_clear_and_set_word() control flow

Return early for errors in pcie_capability_clear_and_set_word_unlocked()
and pcie_capability_clear_and_set_dword() to simplify the control flow.

No functional change intended.

Link: https://lore.kernel.org/r/20230824193712.542167-13-helgaas@kernel.org


Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>