drm/amd/display: Simplify bool conversion

Fix the following coccicheck warning:
./drivers/gpu/drm/amd/display/dc/dcn10/dcn10_hw_sequencer.c:3137:35-40:
WARNING: conversion to bool not needed here

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Suggested-by: Yang Li <oswb@linux.alibaba.com>
Signed-off-by: Abaci Team <abaci-bugfix@linux.alibaba.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>