Check return value from call to core->write(), so in case of
error print error message, jump to goto label fail and eventually
return.

Addresses-Coverity-ID: 1226943
Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: Hans Verkuil <hansverk@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>