um: virt-pci: fix uapi documentation

/**

 * enum virtio_pcidev_ops - virtual PCI device operations

 * @VIRTIO_PCIDEV_OP_RESERVED: reserved to catch errors

 * @VIRTIO_PCIDEV_OP_CFG_READ: read config space, size is 1, 2, 4 or 8;

 *	the @data field should be filled in by the device (in little endian).

 * @VIRTIO_PCIDEV_OP_CFG_WRITE: write config space, size is 1, 2, 4 or 8;

 *	the @data field contains the data to write (in little endian).

 * @VIRTIO_PCIDEV_OP_BAR_READ: read BAR mem/pio, size can be variable;

 * @VIRTIO_PCIDEV_OP_MMIO_READ: read BAR mem/pio, size can be variable;

 *	the @data field should be filled in by the device (in little endian).

 * @VIRTIO_PCIDEV_OP_BAR_WRITE: write BAR mem/pio, size can be variable;

 * @VIRTIO_PCIDEV_OP_MMIO_WRITE: write BAR mem/pio, size can be variable;

 *	the @data field contains the data to write (in little endian).

 * @VIRTIO_PCIDEV_OP_MMIO_MEMSET: memset MMIO, size is variable but

 *	the @data field only has one byte (unlike @VIRTIO_PCIDEV_OP_MMIO_WRITE)