caif: Remove redundant null check before kfree in cfctrl.c

kfree on a null pointer is a no-op.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Acked-by: Sjur Brændeland <sjur.brandeland@stericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>