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().

CRs-Fixed: 2156182
Change-Id: I25794baabf4aac156872d67b910e81a1959e4e99
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>