drm/amd/display: Remove redundant initializers

drm/amd/display: Remove redundant initializers

[WHAT]
Remove unnecessary default value assignments for variables that
are unconditionally assigned before use.

Linux kernel code style prefers no assignments during initialization
when variables are assigned unconditionally as they can obscures
the actual data flow. In addition, compilers will be able to catch them
if variables are used without being updated later in all conditions.

This is reported as UNUSED_VALUE errors by Coverity.

Reviewed-by: Roman Li <roman.li@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>