drm/amd/display: Remove else after return statement in 'dm_update_plane_state'

Else is not necessary after return statements, hence remove it.

Reported by checkpatch:

WARNING: else is not generally useful after a break or return
drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c:9776:
                               return -EINVAL;
                       else

Cc: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Cc: Qingqing Zhuo <qingqing.zhuo@amd.com>
Cc: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>