rapidio: replace rio_free_net() with kfree() in rio_scan_alloc_net()

rapidio: replace rio_free_net() with kfree() in rio_scan_alloc_net()

When idtab allocation fails, net is not registered with rio_add_net() yet,
so kfree(net) is sufficient to release the memory.  Set mport->net to NULL
to avoid dangling pointer.

Link: https://lkml.kernel.org/r/20260121013508.195836-1-lihaoxiang@isrc.iscas.ac.cn
Fixes: e6b585ca6e81 ("rapidio: move net allocation into core code")
Signed-off-by: Haoxiang Li <lihaoxiang@isrc.iscas.ac.cn>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexandre Bounine <alex.bou9@gmail.com>
Cc: Matt Porter <mporter@kernel.crashing.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>