drivers/net/tulip/de4x5.c: fix union member name in DE4X5_GET_REG ioctl

This was previously reported as a security issue due to leakage of
uninitialized stack memory.  Jeff Mahoney pointed out that this is
incorrect since the copied data is from a union (rather than a struct).
Therefore, this patch is only under consideration for the sake of
correctness, and is not security relevant. 

Signed-off-by: Dan Rosenberg <dan.j.rosenberg@gmail.com>
Acked-by: Grant Grundler <grundler@parisc-linux.org>
Signed-off-by: David S. Miller <davem@davemloft.net>