[media] smiapp: Merge smiapp_init() with smiapp_probe()

The smiapp_probe() is the sole caller of smiapp_init(). Unify the two.
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>