caif: Plug memory leak for checksum error

In case of checksum error, the framing layer returns -EILSEQ, but
does not free the packet. Plug this hole by freeing the packet if
-EILSEQ is returned.

Signed-off-by: Sjur Brændeland <sjur.brandeland@stericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>