drm/amd/powerplay: use true, false for bool variable in vega20_hwmgr.c

Fixes coccicheck warning:

drivers/gpu/drm/amd/powerplay/hwmgr/vega20_hwmgr.c:875:1-31: WARNING: Assignment of 0/1 to bool variable

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: zhengbin <zhengbin13@huawei.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>