genetlink: Fix uninitialized variable in genl_validate_assign_mc_groups()

net/netlink/genetlink.c: In function ‘genl_validate_assign_mc_groups’:
net/netlink/genetlink.c:217: warning: ‘err’ may be used uninitialized in this
function

Commit 2a94fe48 ("genetlink: make multicast
groups const, prevent abuse") split genl_register_mc_group() in multiple
functions, but dropped the initialization of err.

Initialize err to zero to fix this.
Signed-off-by: NGeert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/netlink/genetlink.c

@@ -214,7 +214,7 @@ static int genl_validate_assign_mc_groups(struct genl_family *family)
 {
 	int first_id;
 	int n_groups = family->n_mcgrps;
-	int err, i;
+	int err = 0, i;
 	bool groups_allocated = false;
 
 	if (!n_groups)