NFC: nci: Remove redundant assignment to len

Variable 'len' is set to conn_info->max_pkt_payload_len but this
value is never read as it is overwritten with a new value later on,
hence it is a redundant assignment and can be removed.

Clean up the following clang-analyzer warning:

net/nfc/nci/hci.c:164:3: warning: Value stored to 'len' is never read
[clang-analyzer-deadcode.DeadStores]

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>