msm: camera: isp: protect controllable output stream frame skip

Controllable output streams work per frame, thus setting frame skip
does not make sense for them. They also use frame skipping for their
operation, thus arbitrary modification can break it. This change
returns an error if userspace tries to configure frame skip to a
controllable output stream.

Change-Id: I86a2a282550c45cdba551d87377cbbba88a3f50b
Signed-off-by: Petar Sivenov <psiven@codeaurora.org>