drm/amd/display: Removed unused variable 'sdp_stream_enable'

Kernel test robot throws below warning ->

drivers/gpu/drm/amd/amdgpu/../display/dc/dcn31/dcn31_hpo_dp_stream_encoder.c:
In function 'dcn31_hpo_dp_stream_enc_update_dp_info_packets':
   drivers/gpu/drm/amd/amdgpu/../display/dc/dcn31/dcn31_hpo_dp_stream_encoder.c:439:14:
warning: variable 'sdp_stream_enable' set but not used
[-Wunused-but-set-variable]
   439 |         bool sdp_stream_enable = false;

Removed unused variable 'sdp_stream_enable'.

Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Dong Chenchen <dongchenchen2@huawei.com>
Signed-off-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>