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/20250116171650.33585-3-manivannan.sadhasivam@linaro.org
Fixes: 2c156ac ("misc: Add host side PCI driver for PCI test function device")
Reported-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Closes: https://lore.kernel.org/r/YvzNg5ROnxEApDgS@kroah.com
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Niklas Cassel <cassel@kernel.org>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Niklas Cassel <cassel@kernel.org>

Author: Mani-Sadhasivam