media: siano: use DEFINE_MUTEX() for mutex lock and LIST_HEAD for list head

mutex lock can be initialized automatically with DEFINE_MUTEX()
rather than explicitly calling mutex_init().
list head can be initialized automatically with LIST_HEAD()
rather than explicitly calling INIT_LIST_HEAD().

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Ye Bin <yebin10@huawei.com>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>