media: atomisp: drop a cast for a const argument

Some arguments for tnf and ref settings are meant to be const, but
they're defined without such annotation. Due to that, there's an
ugly cast at sh_css_sp.c.

Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>