- Prevent a possible buffer overflow when updating the ring buffer by
    bounds checking the command frame against the available space in the
    ring buffer.

 v2: update the ring_buffer_end address
 v3: update the commit log
 v4: squash in print fix (Michel)
Signed-off-by: Evan Quan <evan.quan@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>