media: v4l: subdev: Rename sub-device state information access functions

Rename the sub-devices state information access functions, removing
"_stream" from them and replacing "format" by "ffmt". This makes them
shorter and so more convenient to use. No other sets of functions will be
needed to access this information.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>