drm/amdgpu/display: fix semicolon.cocci warnings

drivers/gpu/drm/amd/amdgpu/../display/dc/dce/dce_stream_encoder.c:411:23-24: Unneeded semicolon
drivers/gpu/drm/amd/amdgpu/../display/dc/dce/dce_stream_encoder.c:420:39-40: Unneeded semicolon

 Remove unneeded semicolon.

Generated by: scripts/coccinelle/misc/semicolon.cocci

CC: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>