doc: fix documentation about uio_hv_generic

The vmbus sysfs file names changed in
 commit f6b2db08 ("vmbus: make sysfs names consistent with PCI")
and the uio documenatation does not match the current names.

Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>