[media] r820t: Delete an unnecessary variable initialisation in generic_set_freq()

The variable "rc" will be set to an appropriate value from a call of
the r820t_set_tv_standard() function.
Thus let us omit the explicit initialisation at the beginning.

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