hardware/mISDN/mISDNinfineon.c: bail out of loop on error

If setup_instance() fails we kfree() the card, and then use it in the next
loop iteration.  So lets bail out of the loop instead.

Coverity CID: 13357

Signed-off-by: Darren Jenkins <darrenrjenkins@gmail.com>
Cc: Karsten Keil <isdn@linux-pingi.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>