PCI: endpoint: test: Synchronously cancel command handler work

Use cancel_delayed_work_sync() in pci_epf_test_epc_deinit() to ensure
that the command handler is really stopped before proceeding with DMA
and BAR cleanup.

The same change is also done in pci_epf_test_link_down() to ensure that
the link down handling completes with the command handler fully stopped.

Link: https://lore.kernel.org/r/20241017010648.189889-1-dlemoal@kernel.org


Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Reviewed-by: Frank Li <Frank.Li@nxp.com>