drm/amd/powerplay: Fix missing break in switch

commit 2f10d823739680d2477ce34437e8a08a53117f40 upstream.

Add missing break statement in order to prevent the code from falling
through to the default case.

The resoning for this is that pclk_vol_table is an automatic variable.
So, it makes no sense to update it just before falling through to the
default case and return -EINVAL.

This bug was found thanks to the ongoing efforts to enabling
-Wimplicit-fallthrough.

Fixes: cd70f3d6 ("drm/amd/powerplay: PP/DAL interface changes for dynamic clock switch")
Cc: stable@vger.kernel.org
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>