staging: unisys: visornic_resume needs to mirror _serverdown_complete

Previously we simplified the serverdown function to basically turn it
into a dev_close(), but missed the analogous logic in visornic_resume()
(which is essentially the "book-end" of visornic_serverdown_complete()).
As a result, during IO partition recovery, the nic would go closed when
the IO partition went away, but would never be opened again when the IO
partition came back.

This patch changes visornic_resume() to use dev_open(), so that it once
again plays nicely with visornic_serverdown_complete().  Because
dev_open() forces us into the visornic_open() path, other logic in
visornic_resume() was no longer necessary, and lended to simplifying
visornic_resume() even more.

Fixes: 36645d72a377 ("staging: unisys: simplify visornic_serverdown_complete")
Signed-off-by: Tim Sell <Timothy.Sell@unisys.com>
Signed-off-by: Benjamin Romer <benjamin.romer@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>