drm/amd/pm: remove dead code in navi10_emit_clk_levels and navi10_print_clk_levels

Since the range of the varibable i is 0 - 3.
So execution cannot reach this statement: default.

Signed-off-by: Jesse Zhang <Jesse.Zhang@amd.com>
Reviewed-by: Yang Wang <kevinyang.wang@amd.com>
Reviewed-by: Tim Huang <Tim.Huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>