caif-hsi: Fix merge issues.

Fix the failing merge in net-next by reverting the last
net-next merge for caif_hsi.c and then merge in the commit:
"caif-hsi: Bugfix - Piggyback'ed embedded CAIF frame lost"
from the net repository.

The commit:"caif-hsi: Add missing return in error path" from
net repository was dropped, as it changed code previously removed in the
net-next repository.

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