IB/hfi1: Add error checking for buffer overrun in OPA aggregate

Improve safety of code by checking the size of the data buffer and
prevent buffer overrun

Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Reviewed-by: Brian Welty <brian.welty@intel.com>
Signed-off-by: Neel Desai <neel.desai@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>