misc: pci_endpoint_test: Fix IOCTL return value

IOCTLs are supposed to return 0 for success and negative error codes for
failure. Currently, this driver is returning 0 for failure and 1 for
success, that's not correct. Hence, fix it!

Link: https://lore.kernel.org/r/[email protected]
Fixes: 2c156ac ("misc: Add host side PCI driver for PCI test function device")
Reported-by: Greg Kroah-Hartman <[email protected]>
Closes: https://lore.kernel.org/r/[email protected]
Signed-off-by: Manivannan Sadhasivam <[email protected]>
Signed-off-by: Bjorn Helgaas <[email protected]>
Tested-by: Niklas Cassel <[email protected]>
Reviewed-by: Damien Le Moal <[email protected]>
Reviewed-by: Niklas Cassel <[email protected]>

Author: Mani-Sadhasivam