sfc: siena: eliminate xdp_rxq_info_valid using XDP base API

Commit d48523cb ("sfc: Copy shared files needed for Siena (part 2)")
use xdp_rxq_info_valid to track failures of xdp_rxq_info_reg().
However, this driver-maintained state becomes redundant since the XDP
framework already provides xdp_rxq_info_is_reg() for checking registration
status.

Signed-off-by: Fushuai Wang <wangfushuai@baidu.com>
Acked-by: Edward Cree <ecree.xilinx@gmail.com>
Reviewed-by: Larysa Zaremba <larysa.zaremba@intel.com>
Link: https://patch.msgid.link/20250628051033.51133-1-wangfushuai@baidu.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>