drm/amd/display: dc_link: code clean up on detect_dp function

Removes codestyle issues on detect_dp function as suggested by
checkpatch.pl.

CHECK: Lines should not end with a '('
WARNING: Missing a blank line after declarations
WARNING: line over 80 characters
CHECK: Alignment should match open parenthesis

Signed-off-by: Melissa Wen <melissa.srw@gmail.com>
Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Reviewed-by: Zhan Liu <zhan.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>