net: qrtr: Use radix_tree_iter_delete

Use radix_tree_iter_delete instead of radix_tree_delete to properly
remove slots in a radix tree without any dangling references.

Change-Id: Ie72272d467b962538e7fe29b14c5d845308a9c51
Signed-off-by: Chris Lew <clew@codeaurora.org>