3c59x: Remove unused pointer in vortex_eisa_cleanup()

Remove unused network device private data pointer 'vp' in function
vortex_eisa_cleanup(). Detected by Coverity: CID 139826.

Signed-off-by: Christian Engelmayer <cengelma@gmx.at>
Signed-off-by: David S. Miller <davem@davemloft.net>