If there are no channels, chan would never end up being NULL,
and so the null pointer check would fail.

Solve this by initializing chan to NULL, and iterating over temp instead.

Fixes oops when running intel-gpu-tools/tests/kms_flip, which attempts to
do some intel ioctl's on a nouveau device.
Signed-off-by: NMaarten Lankhorst <maarten.lankhorst@canonical.com>
Cc: stable@vger.kernel.org [3.7+]
Signed-off-by: NBen Skeggs <bskeggs@redhat.com>