mISDN: fix possible memory leak in hfcmulti_init()

hc has been allocated in this function and missing free it before
leaving from some error handling cases.

spatch with a semantic match is used to found this problem.
(http://coccinelle.lip6.fr/

)

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: David S. Miller <davem@davemloft.net>