[media] wl128x: fix typo in MODULE_PARM_DESC

The module_param() is "default_rds_buf" and the MODULE_PARM_DESC()
should match.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>