drm/amd/display: Use _free() macro for amdgpu_dm_commit_zero_streams()

All cases except a failure to create a copy of the current context will
call dc_state_release() on the copied context.

Use a _free() macro to free the context and then adjust the error handling
flow to drop the unnecessary use of goto statements.

Reviewed-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Wayne Lin <wayne.lin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>