hwmon: (ibmaem) add missing kfree

rs_resp is dynamically allocated in aem_read_sensor(), so it should be freed
before exiting in every case.  This collects the kfree and the return at
the end of the function.

Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>
Cc: stable@kernel.org # 2.6.27+