staging: vt6656: Use proper target pointer in memcpy()

The coverity scanner marked these two memcpy()'s as causing a buffer
overflow in CIDs 142743 and 142744. This is due the h_dest member of
struct ethhdr being used as a target (size ETH_ALEN) in memcpy, but the
copy is of size ETH_HLEN. However, the intention here seems to be to
copy the entire ethernet header. Make that clear by specifying the
proper destination buffer.

Also remove the unnecessary casts of the source argument.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>