drm/amd/display/dc/link/protocols/link_dp_capability: Remove unused variable...

drm/amd/display/dc/link/protocols/link_dp_capability: Remove unused variable and mark another as __maybe_unused

‘ds_port’ is clearly not used anywhere and ‘result_write_min_hblank’ is
only utilised when debugging is enabled.  The alternative would be to
allocate the variable under the same clause as the debugging code, but
that would become very messy, very quickly.

Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/amd/amdgpu/../display/dc/link/protocols/link_dp_capability.c: In function ‘dp_wa_power_up_0010FA’:
 drivers/gpu/drm/amd/amdgpu/../display/dc/link/protocols/link_dp_capability.c:280:42: warning: variable ‘ds_port’ set but not used [-Wunused-but-set-variable]
 drivers/gpu/drm/amd/amdgpu/../display/dc/link/protocols/link_dp_capability.c: In function ‘dpcd_set_source_specific_data’:
 drivers/gpu/drm/amd/amdgpu/../display/dc/link/protocols/link_dp_capability.c:1296:32: warning: variable ‘result_write_min_hblank’ set but not used [-Wunused-but-set-variable]

Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Leo Li <sunpeng.li@amd.com>
Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: "Pan, Xinhui" <Xinhui.Pan@amd.com>
Cc: David Airlie <airlied@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Wenjing Liu <wenjing.liu@amd.com>
Cc: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Lee Jones <lee@kernel.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>