bnxt_en: Simplify bnxt_xdp_buff_init()

bnxt_xdp_buff_init() does not modify the data_ptr or the len parameters,
so no need to pass in the addresses of these parameters.

Fixes: b231c3f3 ("bnxt: refactor bnxt_rx_xdp to separate xdp_init_buff/xdp_prepare_buff")
Reviewed-by: Andy Gospodarek <andrew.gospodarek@broadcom.com>
Reviewed-by: Somnath Kotur <somnath.kotur@broadcom.com>
Reviewed-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>