rxrpc: Fix error handling in rxgk_extract_token()

rxrpc: Fix error handling in rxgk_extract_token()

Fix a missing bit of error handling in rxgk_extract_token(): in the event
that rxgk_decrypt_skb() returns -ENOMEM, it should just return that rather
than continuing on (for anything else, it generates an abort).

Fixes: 64863f4ca494 ("rxrpc: Fix unhandled errors in rxgk_verify_packet_integrity()")
Closes: https://sashiko.dev/#/patchset/20260422161438.2593376-4-dhowells@redhat.com
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Jeffrey Altman <jaltman@auristor.com>
cc: Simon Horman <horms@kernel.org>
cc: linux-afs@lists.infradead.org
cc: stable@kernel.org
Link: https://patch.msgid.link/20260423200909.3049438-4-dhowells@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>