ethdev: change owner delete function to return int

ethdev: change owner delete function to return int

Change rte_eth_dev_owner_delete() return value from void to int
and return negative errno values in case of error conditions.

Right now there is only one error case for rte_eth_dev_owner_delete() -
invalid owner, but it still makes sense to return error to catch bugs
in the code which uses the function.

Also update the usage of the function in drivers/netvsc
according to the new return type.

Signed-off-by: Igor Romanov <igor.romanov@oktetlabs.ru>
Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>