ipv4: igmp: Remove redundant comparison in igmp_mcf_get_next()

The 'state->im' value will always be non-zero after
the 'while' statement, so the check can be removed.

Found by InfoTeCS on behalf of Linux Verification Center
(linuxtesting.org) with SVACE.
Signed-off-by: Gavrilov Ilia <Ilia.Gavrilov@infotecs.ru>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20230912084039.1501984-1-Ilia.Gavrilov@infotecs.ruSigned-off-by: Paolo Abeni <pabeni@redhat.com>

net/ipv4/igmp.c

@@ -2944,8 +2944,6 @@ static struct ip_sf_list *igmp_mcf_get_next(struct seq_file *seq, struct ip_sf_l
 				continue;
 			state->im = rcu_dereference(state->idev->mc_list);
 		}
-		if (!state->im)
-			break;
 		spin_lock_bh(&state->im->lock);
 		psf = state->im->sources;
 	}