drm/amd/display: Fix unnecessary cast warnings from checkpatch

This patch addresses warnings produced by the checkpatch script
related to unnecessary casts that could potentially hide bugs.

The specific warnings are as follows:
- Warning at drivers/gpu/drm/amd/display/dc/dml2/dml21/dml21_wrapper.c:16
- Warning at drivers/gpu/drm/amd/display/dc/dml2/dml21/dml21_wrapper.c:20
- Warning at drivers/gpu/drm/amd/display/dc/dml2/dml21/dml21_wrapper.c:30

Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Rohit Chavan <roheetchavan@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>