drm/amd/display: add sanity check for clk table from smu
[Why]
Handle the case where we don't get a valid table. Also fixes compiler
warning for variable potentially used before assignment.
[How]
If the entire table has no valid fclk, reject the table and use our own
hard code.
Signed-off-by: Eric Yang <Eric.Yang2@amd.com> Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com> Reviewed-by: Roman Li <Roman.Li@amd.com> Signed-off-by: Alex Deucher <alexander.deucher@amd.com>