fpga: dfl: pci: fix return value of cci_pci_sriov_configure

fpga: dfl: pci: fix return value of cci_pci_sriov_configure

pci_driver.sriov_configure should return negative value on error and
number of enabled VFs on success. But now the driver returns 0 on
success. The sriov configure still works but will cause a warning
message:

  XX VFs requested; only 0 enabled

This patch changes the return value accordingly.

Cc: [email protected]
Signed-off-by: Xu Yilun <[email protected]>
Signed-off-by: Wu Hao <[email protected]>
Signed-off-by: Moritz Fischer <[email protected]>