bt_host_write: fix invalid check
bt_host_write: fix invalid check

r is uninitalised, so this check is undefined. Change it to check len
instead.

Signed-off-by: Joel Stanley <4816dabf8db1bc6cac35b3a24cab2ff844b5b0c7@jms.id.au>

openbmc/btbridge,openbmc/btbridge