hsr: off by one sanity check in hsr_register_frame_in()

This is a sanity check and we never pass invalid values so this patch
doesn't change anything.  However the node->time_in[] array has
HSR_MAX_SLAVE (2) elements and not HSR_MAX_DEV (3).

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>