drm/amd/display: Fix index may exceed array range within fpu_update_bw_bounding_box

[Why]
Coverity reports OVERRUN warning. soc.num_states could
be 40. But array range of bw_params->clk_table.entries is 8.

[How]
Assert if soc.num_states greater than 8.

Reviewed-by: Alex Hung <alex.hung@amd.com>
Acked-by: Tom Chung <chiahsuan.chung@amd.com>
Signed-off-by: Hersen Wu <hersenxs.wu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>