media: media/siano: kill pointless kmutex definitions

Use the mutex api instead of renaming the calls for this
driver.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>