drm/amd/display: code clean up in dce80_hw_sequencer.c

Fix the following gcc warning:

drivers/gpu/drm/amd/amdgpu/../display/dc/dce80/dce80_hw_sequencer.c:43:46:
warning: ‘reg_offsets’ defined but not used [-Wunused-const-variable=]
 static const struct dce80_hw_seq_reg_offsets reg_offsets[] = {
                                              ^~~~~~~~~~~

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