drm/amd/display: codestyle cleanup on dc_link file until detect_dp func

drm/amd/display: codestyle cleanup on dc_link file until detect_dp func

Removes codestyle issues on the file dc_link until detect_dp func as
suggested by checkpatch.pl.

Types covered:

CHECK: Please don't use multiple blank lines
CHECK: Comparison to NULL could be written
ERROR: space required before the open parenthesis '('
CHECK: Alignment should match open parenthesis
CHECK: Lines should not end with a '('
WARNING: please, no space before tabs
WARNING: Comparisons should place the constant on the right side of the test
WARNING: braces {} are not necessary for single statement blocks
CHECK: Please don't use multiple blank lines

Signed-off-by: Melissa Wen <melissa.srw@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>