[media] RedRat3: Improve another size determination in redrat3_reset()

Replace the specification of a data type by a pointer dereference
as the parameter for the operator "sizeof" to make the corresponding size
determination a bit safer.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>