[media] ov7670: fix g/s_parm

Drop unnecesary memset. Drop the unnecessary extendedmode check and
set the V4L2_CAP_TIMEPERFRAME capability.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>