drm/amd/powerplay: remove duplicate include

Remove asic_reg/nbio/nbio_6_1_offset.h which is included more than once

Reviewed-by: Evan Quan <evan.quan@amd.com>
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wang Hai <wanghai38@huawei.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>