media: atomisp: Simplify atomisp_css_[start|stop]()

Now that continuous mode is gone and we only have 1 /dev/video# node,
the videobuf2 core guarantees that atomisp_css_[start|stop]() will
only be called one at a time.

So there is no need for atomisp_streaming_count() counts.

When reqbufs has been done then the streams are guaranteed to be created,
and streaming cannot be started without reqbufs so there is no need for
atomisp_css_start() to check if it needs to create the streams.

Use this to clean-up atomisp_css_[start|stop]().

While at it also fix atomisp_css_start() not re-creating the streams
on an error, breaking the guarantee that the streams are always there
after a succesfull reqbufs call.

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>