PCI: epf-test: Cleanup request result handling

Each of the test functions pci_epf_test_write(), pci_epf_test_read() and
pci_epf_test_copy() return an int result which is used by
pci_epf_test_cmd_handler() to set a success or error bit in the request
status.

In the spirit of keeping the processing of each test case self-contained
within its own test function, move the request status field update from
pci_epf_test_cmd_handler() to each of these test functions and change these
functions declaration to returning void.

Link: https://lore.kernel.org/r/20230415023542.77601-12-dlemoal@kernel.org


Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Manivannan Sadhasivam <mani@kernel.org>