staging: ks7010: Delete a variable in write_to_device()

The local variable "rc" was assigned a zero at one place.
But it was not read within this function. Thus delete it.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Reviewed-by: Wolfram Sang <wsa@the-dreams.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>