GFS2: Fix reference to ERR_PTR in gfs2_glock_iter_next

[ Upstream commit 14d37564 ]

This patch fixes a place where function gfs2_glock_iter_next can
reference an invalid error pointer.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>