ser_gigaset: remove unnecessary kfree() calls from release method

device->platform_data and platform_device->resource are never used
and remain NULL through their entire life. Drops the kfree() calls
for them from the device release method.

Signed-off-by: Tilman Schmidt <tilman@imap.cc>
Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: David S. Miller <davem@davemloft.net>