[media] smiapp: Remove unnecessary BUG_ON()'s

Instead, calculate how much is needed and then allocate the memory
dynamically.

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>