media: em28xx: Don't use ops->suspend if it is NULL

The call to ops->suspend for the dev->dev_next case can currently
trigger a call on a null function pointer if ops->suspend is null.
Skip over the use of function ops->suspend if it is null.

Addresses-Coverity: ("Dereference after null check")

Fixes: be7fd3c3 ("media: em28xx: Hauppauge DualHD second tuner functionality")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>