[WHY]
Check max_tmds_clk_mhz firstly will restrict pixel clock under HDMI
1.4, thus HDMI2.0 port can't correctly support 4K 60Hz.

[HOW]
Fine tune the logic to check max_forum_tmds_clk_mhz firstly.
Signed-off-by: Dale Zhao <dale.zhao@amd.com>
Reviewed-by: Chris Park <Chris.Park@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>