rxrpc: Fix wrong error return in rxrpc_connect_call()

Fix rxrpc_connect_call() to return -ENOMEM rather than 0 if it fails to
look up a peer.

This generated a smatch warning:
        net/rxrpc/call_object.c:303 rxrpc_connect_call() warn: missing error code 'ret'

I think this also fixes a syzbot-found bug:

        rxrpc: Assertion failed - 1(0x1) == 11(0xb) is false
        ------------[ cut here ]------------
        kernel BUG at net/rxrpc/call_object.c:645!

where the call being put is in the wrong state - as would be the case if we
failed to clear up correctly after the error in rxrpc_connect_call().

Fixes: 9d35d880 ("rxrpc: Move client call connection to the I/O thread")
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <error27@gmail.com>
Reported-and-tested-by: syzbot+4bb6356bb29d6299360e@syzkaller.appspotmail.com
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/202301111153.9eZRYLf1-lkp@intel.com/Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
Link: https://lore.kernel.org/r/2438405.1673460435@warthog.procyon.org.ukSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/rxrpc/call_object.c

@@ -294,7 +294,7 @@ static void rxrpc_put_call_slot(struct rxrpc_call *call)
 static int rxrpc_connect_call(struct rxrpc_call *call, gfp_t gfp)
 {
 	struct rxrpc_local *local = call->local;
-	int ret = 0;
+	int ret = -ENOMEM;
 
 	_enter("{%d,%lx},", call->debug_id, call->user_call_ID);