net: qualcomm: rmnet: Remove unnecessary device assignment

Device of the de-aggregated skb is correctly assigned after inspecting
the mux_id, so remove the assignment in rmnet_map_deaggregate().

Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>
Signed-off-by: David S. Miller <davem@davemloft.net>