dca: remove unneeded NULL check

The return here doesn't release the locks or re-enable IRQs.  But as
Andrew Morton points out, domain is never NULL.  list_first_entry()
essentially never returns NULL and also we already verified that the list
is not empty.
Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Maciej Sosnowski <maciej.sosnowski@intel.com>
Cc: David Miller <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/dca/dca-core.c

@@ -110,8 +110,6 @@ static void unregister_dca_providers(void)
 
 	/* at this point only one domain in the list is expected */
 	domain = list_first_entry(&dca_domains, struct dca_domain, node);
-	if (!domain)
-		return;
 
 	list_for_each_entry_safe(dca, _dca, &domain->dca_providers, node) {
 		list_del(&dca->node);