drm/amd/amdgpu: Update debugfs link_settings output link_rate field in hex

link_rate is updated via debugfs using hex values, set it to output
in hex as well.

eg: Resolution: 1920x1080@144Hz
cat /sys/kernel/debug/dri/0/DP-1/link_settings
Current:  4  0x14  0  Verified:  4  0x1e  0  Reported:  4  0x1e  16  Preferred:  0  0x0  0

echo "4 0x1e" > /sys/kernel/debug/dri/0/DP-1/link_settings

cat /sys/kernel/debug/dri/0/DP-1/link_settings
Current:  4  0x1e  0  Verified:  4  0x1e  0  Reported:  4  0x1e  16  Preferred:  4  0x1e  0

Signed-off-by: Anson Jacob <Anson.Jacob@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>