ipv6: mcast: Remove redundant comparison in igmp6_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.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Gavrilov Ilia <[e-mail]>
Reviewed-by: David Ahern <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Paolo Abeni <[e-mail]>

net/ipv6/mcast.c

···
 				continue;
 			state->im = rcu_dereference(state->idev->mc_list);
 		}
-		if (!state->im)
-			break;
 		psf = rcu_dereference(state->im->mca_sources);
 	}
 out: