drm/amdgpu: use true, false for bool variable in mxgpu_nv.c

Fixes coccicheck warning:

drivers/gpu/drm/amd/amdgpu/mxgpu_nv.c:255:2-20: WARNING: Assignment of 0/1 to bool variable
drivers/gpu/drm/amd/amdgpu/mxgpu_nv.c:267:2-20: 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>